Acromag Busworks 900mb series User manual

BusWorks



900MB Series

Modbus/RS485 Network I/O Modules

Model 901MB/902MB/903MB Digital Input/Output

With Sinking Outputs And Active-Low Inputs

USER’S MANUAL

ACROMAG INCORPORATED

30765 South Wixom Road

P.O. BOX 437

Wixom, MI 48393-7037 U.S.A.

Tel: (248) 295-0880

Fax: (248) 624-9234

Data and specifications are subject to change without notice.

8500-631-J12F005

BusWorksModel 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O

___________________________________________________________________________________________

- 2 -

Safety Summary - Symbols on equipment:

Means “Caution, refer to this manual for additional

information”.

The information contained in this manual is subject to change

without notice. Acromag, Inc., makes no warranty of any kind

with regard to this material, including, but not limited to, the

implied warranties of merchantability and fitness for a particular

purpose. Further, Acromag, Inc., assumes no responsibility for

any errors that may appear in this manual and makes no

commitment to update, or keep current, the information contained

in this manual. No part of this manual may be copied or

reproduced in any form, without the prior written consent of

Acromag, Inc.

Table of Contents

Page

1.0

INTRODUCTION

………………………………..…….. 2

DESCRIPTION ………………………………………… 2

Key 903MB Features……………………………….. 3

ACCESSORY ITEMS …………………………………. 3

2.0

PREPARATION FOR USE

….……………………….. 4

UNPACKING AND INSPECTION ……………………

MODULE INSTALLATION.……………..…………….. 4

Default Mode Switch………………………………… 4

Pullup Installation & Removal………………………. 5

Mounting ……………………………………………… 5

Electrical Connections ……………………………… 5

SOFTWARE INSTALLATION ……………….……….. 6

3.0

MODULE CONFIGURATION

……………………….. 6

AN INTRODUCTION TO MODBUS………………..... 8

MODULE SOFTWARE CONFIGURATION…………. 15

Starting The Program…..…………………………… 16

Creating A Configuration File……………………….. 17

Testing Your Configuration….……………………… 18

4.0

THEORY OF OPERATION

………………………….. 19

5.0

SERVICE AND REPAIR

…………………………..… 19

SERVICE AND REPAIR ASSISTANCE ……………. 19

PRELIMINARY SERVICE PROCEDURE ..…………. 19

TROUBLESHOOTING………………………………… 19

6.0

SPECIFICATIONS

……………………………………. 20

MODEL NUMBER DEFINITION……………………… 20

I/O SPECIFICATIONS……………….…………..……. 20

ENCLOSURE/PHYSICAL SPECIFICATIONS..…….. 21

APPROVALS ………………………………………….. 21

ENVIRONMENTAL SPECIFICATIONS….………….. 21

COMMUNICATION INTERFACE SPECIFICATIONS 22

CONFIGURATION AND CONTROLS..……………... 22

SOFTWARE CONFIGURATION……..…………….… 22

List of Drawings Page

Simplified Schematic (4501-809)…..…….……………..… 24

Functional Block Diagram (4501-810)………………….… 24

Pullup Resistor SIP Locations (4501-811)……………….. 25

Network Connections (4501-805)…………..…….………. 25

Electrical Connections Page 1 of 4 (4501-813)……..…... 26

Electrical Connections Page 2 of 4 (4501-813)……..…... 26

Electrical Connections Page 3 of 4 (4501-813)……..…... 27

Electrical Connections Page 4 of 4 (4501-813)……..…... 27

Interposing Relay Conn. & Contact Pro. (4501-814)……. 28

Enclosure Dimensions (4501-815) …………………..…… 28

Windows 95/98 & NT are registered trademarks of Microsoft

Corporation. Modbus is a registered trademark of Modicon, Inc.

IMPORTANT SAFETY CONSIDERATIONS

It is very important for the user to consider the possible adverse

effects of power, wiring, component, sensor, or software failures

in designing any type of control or monitoring system. This is

especially important where economic property loss or human life

is involved. It is important that the user employ satisfactory

overall system design. It is agreed between the Buyer and

Acromag, that this is the Buyer's responsibility.

1.0 INTRODUCTION

These instructions cover the hardware functionality of the

transmitter models listed in Table 1. Supplementary sheets are

attached for units with special options or features.

Table 1: Models Covered in This Manual

Series/

Input Type

Options/Output/

Enclosure/ Approvals

Factory

Config

I/O Type

901MB -0900 -C 12 Inputs

902MB -0900 -C 12 Outputs

903MB -0900 -C 12 In/Out

Notes (Table 1):

1. Agency approvals include CE, UL Listed, and cUL Listed.

2. Include the “-C” suffix to specify factory configuration option.

Otherwise, no suffix is required for standard configuration.

3. The 903MB includes both inputs and outputs, while the

902MB is output only, and the 901MB is input only.

The same circuit board is used to build all three models

listed. The fully populated 903MB model includes tandem input

and output circuits. Input circuitry is removed for 902MB models

which are output only, and output circuitry is removed for 901MB

models which are input only.

DESCRIPTION

The Acromag 900MB family is a group of process I/O

modules and accessories for Modbus/RS485 network I/O

applications. The 901MB/902MB/903MB models support up to

twelve buffered inputs and/or open-drain outputs according to the

model number. Inputs are active-low and outputs are current-

sinking low-side switches. These models are the complement of

Acromag 904MB/905MB/906MB modules which have open-

source high-side output switches and active-high inputs. The

900MB modules contain an advanced technology microcontroller

with integrated downloadable flash memory and EEPROM for

non-volatile program, configuration, and parameter data storage.

Units are fully reconfigurable via our user-friendly Windows

95/98



or NT



Configuration Program and the RS485 interface.

Once configured, these modules may operate as active RS485

network slaves connected to other modules and a host computer

performing network I/O functions.

The Model 901MB supports up to 12 digital inputs. The

Model 902MB drives up to 12 digital outputs. The Model 903MB

supports up to 12 tandem digital input and output channels.

Each 900MB module provides an isolated RS485 network I/O

path utilizing the Modbus protocol. Socketed I/O pullup resistors

are installed and pull the I/O channels up to the EXC+ terminal.

These resistors may be easily removed or exchanged according

to your application requirements.

BusWorksModel 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O

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I/O channels include yellow LED’s on the front of the module that

provide visual indication of channel state. Additionally, a green

“Run” and yellow “Status” LED provides local feedback of

operating mode, system diagnostics, watchdog timeout

indication, and module status.

All 900MB modules are designed to withstand harsh

industrial environments. They feature RFI, EMI, ESD, EFT, and

surge protection, plus low temperature drift, wide ambient

temperature operation, and isolation between input, outputs,

power, and the network. They also have low radiated emissions

per CE requirements. As a wide-range DC-powered device, the

unit may be powered from DC power networks incorporating

battery backup. Since the input is diode bridge coupled, the unit

may be connected to redundant power supplies, or several units

may safely share a single DC supply. The unit may also be

powered from common 24VAC power.

Units are DIN-rail mounted and removable terminal blocks

facilitate ease of installation and replacement, without having to

remove wiring. Module power and network wiring are inserted at

one side of the unit, while I/O wiring is inserted at the other side.

Module connectors are an industry standard screw clamp type

that accept a wide range of wire sizes.

Flexible transmitter functionality, network reprogrammability,

mixed signal I/O, watchdog support, and a network interface, are

all combined in a single package to make this instrument

extremely powerful and useful over a broad range of applications.

Further, the safe, compact, rugged, reconfigurable, and reliable

design of this transmitter makes it an ideal choice for control

room or field applications. Custom module configurations are

also possible (please consult the factory).

Key 903MB Module Features:

•Agency Approvals - CE, UL, & cUL Listed.

•Easy Windows



Configuration - Fully reconfigurable via

our user-friendly Windows 95/98



or NT



900MB

Configuration Program.

•RS485/Modbus Network Interface - This proven high

speed interface is highly immune to noise, can operate over

long distances, and allows a large number of modules to be

networked together. The unit communicates using the

industry-standard Modbus command/response protocol.

•Nonvolatile Reprogrammable Memory - This module has

an advanced technology microcontroller with integrated,

non-volatile, downloadable flash memory and EEPROM.

This allows the functionality of this device to be reliably

reprogrammed thousands of times.

•Fully Isolated – I/O circuitry, network, & power are isolated

from each other for safety and increased noise immunity.

•Flexible Discrete Inputs and Outputs - High voltage, high

current, open-drain outputs provide direct (low-side) control

of external devices. High voltage buffered inputs allow

outputs to be read back, or input levels to be monitored.

•Outputs Have Built-in Protection – Outputs include over-

temperature and over-current shut-down protection, plus

active clamping circuitry for switching inductive loads.

•Tandem Input/Output Circuitry (903MB Units) - Input

buffers are connected in tandem with open-drain outputs for

convenient loopback monitoring of the output state.

•High-Speed Data Rates – Supports half-duplex RS485

baud rates up to 115K baud.

Key 903MB Module Features…continued:

•Convenient Pullup Resistors Mounted In Sockets – SIP

resistors are installed in sockets on the board and provide

input/output pullup functionality. These SIP resistors can be

easily removed or exchanged according to your application.

•Self-Diagnostics - Built-in routines operate upon power-up

for reliable service, plus easy maintenance and trouble-

shooting. A watchdog timer is also built into the micro-

controller that causes it to initiate a self reset if it ever fails to

return from an operation in a timely manner or “locks up”.

•I/O Watchdog Timer – This function is included and may be

configured for timeout periods up to 65534 seconds (18.2

hours). A timeout will occur if no port channel I/O has taken

place for the specified time period. Optionally, the digital

outputs can be automatically set to a user-defined state

following a watchdog timeout. A port timeout is cleared via

a read or write to a port I/O channel. Watchdog control of

an output state has higher priority than direct control.

•Wide-Range DC or 24VAC Power - This device receives

power over a wide supply range and the power terminals are

diode-bridge coupled. This makes this transmitter useful for

systems with redundant supplies, and/or battery back-up.

Additionally, the power terminals are not polarized.

•Wide Ambient Operation - The unit is designed for reliable

operation over a wide ambient temperature range.

•Hardened For Harsh Environments - The unit will operate

reliably in harsh industrial environments and includes

protection from RFI, EMI, ESD, EFT, and surges, plus low

radiated emissions per CE requirements.

•Convenient Mounting, Removal, & Replacement - The

DIN-rail mount and plug-in type terminal blocks make

module removal and replacement easy.

•LED Indicators - A green LED indicates power. A flashing

yellow status LED indicates the unit is in the default

communication mode and/or a watchdog timer timeout has

occurred. Yellow LED’s also indicate the I/O state (active-

low) of the associated open-drain output and/or digital input.

•Default Communication Mode - A push-button switch is

provided to set the module to a default set of communication

parameters for baud rate, module address, parity, and

number of stop bits. This provides a convenient way of

establishing communication with the module when its

internal settings are unknown.

ACCESSORY ITEMS

The following accessories are available from Acromag.

Acromag also offers other standard and custom transmitters and

alarms to serve a wide range of applications (consult the factory).

900MB Configuration & Control Software (Model 5034-186)

Series 900MB modules are configured with this user-friendly

Windows 95/98



or NT



Configuration Program. Optionally, any

software that supports the Modbus/RTU protocol may be used to

configure and control Series 900MB modules, but the use of this

software makes getting started easier. All module functions are

programmable and downloadable to the modules via this

software. The software also includes on-line help. Non-volatile

memory provides program and configuration storage within the

module. Note that this software may be optionally downloaded

from our website (www.acromag.com) to registered owners of

Series 900MB modules.

BusWorksModel 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O

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RS-232 to RS-485 Serial Adapter (Model 5034-214)

This device is a non-isolated, port-powered, signal converter

for communication between the RS-232 serial port of a personal

computer and the RS-485 network interface of Series 900MB I/O

Modules. It is used in conjunction with the Acromag

Configuration Software for simple reconfiguration, testing, and

troubleshooting of Series 900MB I/O modules. As a port-

powered device, it is not intended for driving fully loaded RS-485

networks over long distances, and does not have sufficient power

to drive terminated networks. The adapter has DB-9F connectors

at both ends and plugs directly into the common DB-9M serial

port connector of most personal computers. The module is

connected to the RS-485 side of this adapter via a separate

interconnecting cable (see Cable 5034-202 described below).

Interface Cable (Model 5034-202)

This 3-wire cable is used to connect the RS-485 side of

Signal Converter 5034-214 to the RS-485 network terminals of

Series 900MB modules. This cable is 8 feet long and has a

DE-9M connector on one end, and three stripped and tinned

wires on the other end. The wires are labeled A, B, and C for

connection to the module D, Dbar, and COM terminals,

respectively.

Series 900MB Software Interface Package (Model 900C-SIP)

The 900C-SIP Software Interface Package combines the

900MB Configuration Software (5034-186), RS-232 to RS-485

Serial Converter (5034-214), Interface Cable (5034-202), and

Instructions (8500-649), into a complete kit for interfacing with

Series 900MB I/O Modules.

2.0 PREPARATION FOR USE

UNPACKING AND INSPECTION

Upon receipt of this product, inspect the shipping carton for

evidence of mishandling during transit. If the shipping carton is

badly damaged or water stained, request that the carrier's agent

be present when the carton is opened. If the carrier's agent is

absent when the carton is opened and the contents of the carton

are damaged, keep the carton and packing material for the

agent's inspection. For repairs to a product damaged in

shipment, refer to the Acromag Service Policy to obtain return

instructions. It is suggested that salvageable shipping cartons

and packing material be saved for future use in the event the

product must be shipped.

This module is physically protected

with packing material and electrically

protected with an anti-static bag during

shipment. However, it is

recommended that the module be

visually inspected for evidence of

mishandling prior to applying power.

This circuit utilizes static sensitive

components and should only be

handled at a static-safe workstation.

MODULE INSTALLATION

This transmitter module is packaged in a general purpose

plastic enclosure. Use an auxiliary enclosure to protect the unit in

unfavorable environments or vulnerable locations, or to maintain

conformance to applicable safety standards. Stay within the

specified operating temperature range. As shipped from the

factory, the unit is calibrated for all valid input ranges and has the

default configuration shown in Table 2 below:

WARNING: Applicable IEC Safety Standards may require that

this device be mounted within an approved metal enclosure or

sub-system, particularly for applications with exposure to voltages

greater than or equal to 75VDC or 50VAC.

Table 2: 903MB Default Factory Configuration

PARAMETER

CONFIGURATION

Module Address 247

Baud Rate 9600bps

Parity None

Stop Bits 1 or 2 (When Parity = None)

Response Delay 0 (No Additional Delay)

Watchdog Time (Each Port) 0 (Disabled)

Timeout State (Each Port) 65535 (FFFFH) = No Change

Pullup Resistor To EXC+ 5.6K Installed (In Sockets)

Note: Do not confuse the Default Factory Configuration noted

above with the Default Communication Mode, which refers to the

fixed baud rate, module address, parity, and stop bit settings

achieved by pushing the Default Mode button until the status LED

flashes ON/OFF. The Default Communication Mode will

temporarily over-ride any factory configuration of baud rate,

module address, parity, and stop bits with settings of 9600bps,

247, None, and 1 or 2, respectively. It is provided as a

convenient means of achieving communication with a module

when these parameters are unknown.

Your application will typically differ from the default factory

configuration and will require that the transmitter be reconfigured

to suit your needs. This can be easily accomplished with

Acromag’s user-friendly Windows 95/98



or NT



900MB

Configuration Program. Configuration is normally done prior to

field installation. Refer to MODULE SOFTWARE

CONFIGURATION of Section 3.0 for detailed instructions.

Default Mode Switch

A push-button default mode switch (DFT) and status LED are

provided at the front of the module as a convenient way of

communicating with the module when its baud rate and address

settings are unknown. Push & hold this button until the Status

LED flashes ON/OFF to indicate the module is in the Default

Communication Mode with a fixed module address of 247, baud

rate of 9600bps, no parity, and 1 or 2 stop bits. It is most

convenient to configure a module in this mode, then leave the

default mode by pressing this button again until the Status LED

stops flashing (constant ON or OFF), or by resetting the module.

Note that a rapidly flashing Status LED indicates a watchdog

timer timeout has occurred and this may temporarily mask default

mode indication. The Default Mode is disabled following a

software or power-on reset. New communication parameters (for

baud rate, address, and parity) will take effect following a reset of

the module and the module will leave the Default Mode.

BusWorksModel 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O

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Pullup Installation & Removal (See Drawing 4501-811)

Sockets are installed on the board to accept SIP resistor

networks for optional I/O pullup installation. One 8-pin SIP

socket is provided for every four I/O channels (port). These 8-pin

sockets accept SIP’s of four isolated resistors with the even-

numbered socket pins in common with the EXC+ terminal. Three

5.6KΩresistor SIP’s are installed from the factory, but may be

changed or removed as required by your application. The cover

must be removed to access these sockets (see Drawing

4501-811). For the 5.6K resistor SIP provided, power must be

limited to less than 0.4W per resistor element. Limit excitation

voltages to 35V or less, and drain currents to less than 0.5A.

Your choice of SIP resistor may further limit current and voltage

according to its power rating (ratings of 0.2W, 0.3W, or 0.4W per

resistor element are typical). Refer to the I/O Specifications

section for recommended resistor types and suppliers.

IMPORTANT: You must provide I/O excitation to operate the

outputs and prevent inputs from floating. You may utilize the

internal 5.6K pullup resistors installed in sockets on the board by

connecting a 5-35V excitation supply to the port EXC & RTN

terminals to complete the circuit. Optionally, the internal pullups

may be removed and the I/O terminals can be wired to an

external pullup or load/excitation circuit in similar fashion.

If your application delivers power to the I/O terminal rather than

the port excitation terminal, then the port pullups should be

removed to avoid coupling currents to adjacent port channels via

the pullup resistors.

Outputs are the open drains of n-channel mosfets in series with

output pullup resistors tied in common to the port EXC terminal.

Input circuits utilize these same pullups to the port EXC terminal.

Failure to complete this circuit by providing an excitation supply

and/or pullups will leave the inputs and outputs floating and/or

inoperable (Refer to Simplified Schematic 4501-809).

Mounting

Refer to Enclosure Dimensions Drawing 4501-815 for

mounting and clearance dimensions.

DIN Rail Mounting: This module can be mounted on "T" type

DIN rails. Use suitable fastening hardware to secure the DIN rail

to the mounting surface. Units may be mounted side-by-side on

1-inch centers for limited space applications.

"T" Rail (35mm), Type EN50022: To attach a module to this

style of DIN rail, angle the top of the unit towards the rail and

locate the top groove of the adapter over the upper lip of the rail.

Firmly push the unit towards the rail until it snaps solidly into

place. To remove a module, first separate the input terminal

block(s) from the bottom side of the module to create a clearance

to the DIN mounting area. Next, insert a screwdriver into the

lower arm of the DIN rail connector and use it as a lever to force

the connector down until the unit disengages from the rail.

Electrical Connections

Digital I/O, network, and power terminals can accommodate

wire from 12-24 AWG, stranded or solid copper. Strip back wire

insulation 1/4-inch on each lead before installing into the terminal

block. Since common mode voltages can exist on signal wiring,

adequate wire insulation should be used and proper wiring

practices followed.

It is recommended that I/O, network, and power wiring be

separated for safety, as well as for low noise pickup. Note that

I/O, network, and power terminal blocks are an industry-standard

plug-in type that can be easily removed to facilitate module

removal or replacement, without removing individual wires. Be

sure to remove power before unplugging the terminals to uninstall

the module, or before attempting service. All connections must

be made with power removed.

CAUTION:

Risk of Electric Shock - More than one

disconnect switch may be required to de-energize the

equipment before servicing.

1. Power: Refer to Electrical Connections Drawing 4501-813.

Variations in power supply voltage within rated limits has

negligible effect on module accuracy. For supply

connections, use No. 14 AWG wires rated for at least 75°C.

The power terminals are diode bridge-coupled and not

polarized. Unit is powered from 10-36VDC, or 24VAC only.

2. Digital I/O: Connect I/O per Electrical Connections Drawing

4501-813. Observe proper polarity when making I/O

connections (see label for input type). All outputs are the

open-drains of n-channel mosfets whose source terminals

share return (RTN). I/O pullup resistor SIP’s are installed in

sockets on the board and connected to the port EXC+

terminal. All terminals include transient voltage suppression

and integrated snubbers, but may require additional

protection when switching inductive loads (see below). Refer

to the SPECIFICATIONS section for output specifications

and see the module side label for terminal designations.

Note that outputs are for current-sinking (low-side switching)

applications only. Inputs are active-low. The I/O circuitry is

electrically isolated from the power and network circuits. If

necessary, an interposing relay can be used to switch higher

currents as illustrated in the Interposing Relay Connection

Drawing 4501-814.

Note: Outputs go to their OFF state following a software or

power-on reset of the module. Outputs may be optionally

sent to user-defined states following a watchdog timeout.

IMPORTANT - Protection With Inductive Loads: The

output DMOS type mosfets have integrated shunt diode

clamps connected from drain to source to help protect the

output switch from damaging reverse emf voltages that are

generated when switching inductive loads. You are

encouraged to add external protection local to the inductive

load for added protection and to prevent this emf from being

distributed across the connection media. For DC inductive

loads, place a diode across the load (1N4006 or equivalent)

with cathode to (+) and anode to (-).

3. Network Connections: Wire network as shown in Network

Connections Drawing 4501-805. Network common (COM)

should connect to earth ground at one point.

4. Grounding: See Electrical Connections Drawing 4501-813.

The module housing is plastic and does not require an earth

ground connection.

WARNING: For compliance to applicable safety and

performance standards, the use of shielded cable is

recommended as shown in Drawing 4501-813. Further, the

application of earth ground must be in place as shown in

Drawing 4501-813. Failure to adhere to sound wiring and

grounding practices may compromise safety & performance.

BusWorksModel 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O

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SOFTWARE INSTALLATION - USING SETUP.EXE

The 900MB Configuration Software (Model 900C-SIP) is used

to configure Series 900MB modules and is installed as follows:

1. Start Windows 95/98/NTand insert the 900MB

Configuration Software CDROM into your drive D: (or E:).

IMPORTANT: Before continuing with installation, be sure to

exit any other Windows programs that may be running.

2. Click on the [START] button in the lower left hand corner of

the Windows screen. Then click on the “Run…” icon.

3. In the Run dialogue box, type d:\setup (or e:\setup) in the

Open field and click on [OK]. The setup program will

execute the Installshield Wizard.

You may need to click on the “Setup.exe” icon of the install

shield to proceed. On some machines, the setup.exe

program is not started automatically.

4. From the introductory Acromag 900MB Setup Screen, click

on [Next>] to proceed.

5. At this point, the 900MB Setup program will prompt you for

your “Name” and “Company”. Fill in this information, then

click on [Next>].

6. Now you will be prompted for a destination directory. You

may click on [Browse] to change the default directory, or

[Next>] to accept “C:\ProgramFiles\Acromag\900MB” as the

default. You may also click on [Back] to return to the prior

screen and make any changes.

7. At this point you will be prompted for a program folder name.

You may type a new name, use the scroll bar to select an

existing program folder, or click on [Next>] to accept the

“Acromag 900MB” default folder name.

8. Now you will be presented with your selections and you

should verify if they are correct. Press [Next>] to continue

and begin copying files, or press [Back] to return to prior

screens and make any changes.

9. After the Configuration Program files have been copied to

your hard drive, you will be prompted to click on [Finish] to

complete the setup.

10. Now click on the [Acromag 900MB] program folder icon at

the bottom of your windows screen, then click on the

Acromag 900MB program icon to start the Configuration

Program (Programs-Acromag 900MB-Acromag 900MB

Configuration icon).

3.0 MODULE CONFIGURATION

This module needs to be configured for your application.

Configuration is easily accomplished using Acromag’s Windows

95/98



or NT



Modbus Configuration Software and an RS232-to-

RS485 signal converter. It is not required to use the Acromag

software to communicate with the Series 900MB, as any software

capable of sending Modbus protocol commands over an RS485

network can be used. However, the Acromag software provides

an easy to use Windows format for communicating with the

module that does not require advanced familiarity with the

Modbus protocol.

Modbus registers are organized into the following reference

types identified by the leading number of the reference address:

Reference

Description

0xxxx Read/Write Discrete Outputs or Coils. A 0x

reference is used to drive output data to a digital

output channel.

1xxxx Read Discrete Inputs. The ON/OFF status of a 1x

reference is controlled by the corresponding

digital input channel.

3xxxx Read Input Registers. A 3x reference register

contains a 16-bit number received from an

external source—e.g. an analog signal.

4xxxx Read/Write Output or Holding Registers. A 4x

(binary or decimal), or to send the data from the

CPU to an output channel.

Notes:

1. The “x” following the leading character represents a four-

digit address location in user data memory. The leading

character is generally implied by the function code and

omitted from the address specifier for a given function. The

leading character identifies the I/O data type.

2. The ON/OFF state of discrete inputs and outputs is

represented by a 1 or 0 value assigned to an individual bit in

a 16-bit data word. This is sixteen 0x or 1x references per

data word. With respect to mapping, the LSB of the word

maps to the lowest numbered channel of a group and

channel numbers increase sequentially as you move

towards the MSB. Unused bit positions are set to zero.

The table below outlines the register map for Model

901MB/902MB/903MB network I/O modules. Modbus functions

operate on these registers (except for the Reset Slave and

Report Slave ID functions).

Model 903MB-0900 Register Map

Ref Addr. Description Data Type/Format

Coil Registers (0x References, Read/Write)

0001

Thru

00012

0-11

(0000-

000B)

Twelve

Discrete

Outputs 0-11

(903MB &

902MB Only)

Discrete Output Value.

Addresses a specific bit of

a 16-bit word that controls/

monitors the ON/OFF

status for the output (the

gate signal of the n-

channel mosfet).

Note: This signal corresponds to

the gate signal of the n-channel

output mosfet. Thus, a read of

this register may not reflect the

actual output level at the drain of

the mosfet if the open-drain is not

pulled up or is left floating.

Excitation must be provided in

order to operate the outputs. On

903MB units, you can read the

Contact Registers to obtain the

actual output state(s) via closed

loop feedback.

After reset, these registers read 0

(outputs OFF) and these

registers are not maintained in

EEPROM.

A set bit (1) means the

corresponding output is

turned ON (sinking

current). A clear bit (0)

means the corresponding

output is turned OFF

(open). The bit position

also corresponds to the

output channel number (i.e.

output 0 uses bit 0 of the

16-bit word at address 0,

output 1 uses bit 1 of the

16-bit word at address 1,

etc.) Unused bits are set

to 0.

Bits 15-12: Not Used.

Additionally, unused bits

in range 11-0 are set to 0.

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Model 903MB-0900 Register Map…continued

Ref Addr. Description Data Type/Format

Contact Registers (1x References, Read-Only)

0001

Thru

10012

0-11

(0000-

000B)

Twelve

Discrete

Inputs 0-11

(903MB &

901MB Only)

Discrete Input Value.

Addresses a specific bit of

a 16-bit word that monitors

the ON/OFF status for the

input (or tandem output).

Note: This signal reflects the

actual state of the corresponding

input signal (901MB & 903MB),

or the drain of the tandem output

(903MB). This signal is active-

low.

Failure to install I/O pullups or

provide port excitation will leave

inputs floating.

A set bit (1) means the

corresponding input is ON

(active-low). A clear bit (0)

means the corresponding

input is OFF (high). The bit

position corresponds to the

input channel number (i.e.

input 0 uses bit 0 of the 16-

bit word at address 0, input

1 uses bit 1 of the 16-bit

word at address 1, etc.)

Unused bits of a word are

set to 0.

Bits 15-12: Not Used.

Additionally, unused bits in

range 11-0 are set to 0.

Input Registers (3x References, Read-Only)

30001 0000 Module

Status

Bit 15: Flash Checksum

1 = Error Flag

0 = No Flash Error

Bit 14: Zero (Not Used)

Bit 13: Default Mode Flag

1 = Default Mode Indicator

0 = Not Default Mode

Bits 12-3: Zero

Bit 2: Port 2 (CH 8-11)

1 = Port 2 Watchdog Fault

Bit 1: Port 1 (CH 4-7)

1 = Port 1 Watchdog Fault

Bit 0: Port 0 (CH 0-3)

1 = Port 0 Watchdog Fault

Holding Registers (4x References, Read/Write)

Note: Changes to Holding Registers take effect following the

next software or power-on reset of the module.

0001 0

(0000)

Slave

Address

Default=247

1-247

0002 1

(0001)

Baud Rate

Default=2,

9600bps

0 = 2400bps

1 = 4800bps

2 = 9600bps (Default)

3 = 14400bps

4 = 19200bps

5 = 28800bps

6 = 38400bps

7 = 57600bps

8 = 76800bps

9 = 115200bps

0003 2

(0002)

Parity

Default=

0, None

0 = None (1 or 2 stop bits)

1 = Odd Parity Checking

2 = Even Parity Checking

Model 903MB-0900 Register Map…continued

Ref Addr. Description Data Type/Format

40004 3

(0003)

Port 0

(CH0-3)

Watchdog

Time

Default=0,

Disabled

Can be set from 1 to 65534

seconds. Set to 65535

(FFFFH) or 0 (0000H) to

disable the watchdog timer.

Note: A port timeout can only be

cleared via a read or write to any

channel of the same port, or

upon a software or power-on

reset of the module.

40005 4

(0004)

Port 1

(CH 4-7)

Watchdog

Time

Default=0,

Disabled

Can be set from 1 to 65534

seconds. Set to 65535

(FFFFH) or 0 (0000H) to

disable the watchdog timer.

40006 5

(0005)

Port 2

(CH 8-11)

Watchdog

Time

Default=0,

Disabled

Can be set from 1 to 65534

seconds. Set to 65535

(FFFFH) or 0 (0000H) to

disable the watchdog timer.

40007 6

(0006)

Port 0

(CH 0-3)

Timeout

State

(902MB and

903MB Only)

Default=

65535,

Disabled.

The four lower order bits of

this 16-bit register value

define the state the output

channels of the port will be

programmed to following a

watchdog timeout. Bit 0

corresponds to channel 0,

bit 1 to channel 1, bit 2 to

channel 2, and bit 3 to

channel 3.

Note: Clearing a timeout via an

I/O read or write does not return

the output(s) to their initial state.

They remain in their timeout

states until otherwise written.

Write 65535 (FFFFH) to

this register to leave the

outputs unchanged

following a timeout (this is

also the default value).

40008 7

(0007)

Port 1

(CH 4-7)

Timeout

State

(902MB and

903MB Only)

Default=

65535,

Disabled.

The four lower order bits of

this 16-bit register value

define the state the output

channels of the port will be

programmed to following a

watchdog timeout. Bit 0

corresponds to channel 4,

bit 1 to channel 5, bit 2 to

channel 6, and bit 3 to

channel 7. Write 65535

(FFFFH) to this register to

leave the outputs

unchanged following a

timeout (this is also the

default value).

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Model 903MB-0900 Register Map…continued

Ref Addr. Description Data Type/Format

Holding Registers (4x References, Read/Write)

40009 8

(0008)

Port 2

(CH 8-11)

Timeout

State

(902MB and

903MB Only)

Default=

65535,

Disabled.

The four lower order bits of

this 16-bit register value

define the state the output

channels of the port will be

programmed to following a

watchdog timeout. Bit 0

corresponds to channel 8,

bit 1 to channel 9, bit 2 to

channel 10, and bit 3 to

channel 11. Write 65535

(FFFFH) to this register to

leave the outputs

unchanged following a

timeout (this is also the

default value).

0010 9

(0009)

Response

Delay Time

(Turnaround

Delay)

Default=0,

No Delay

Can be set from 0 to 65500

ticks (1 tick = 1.085us).

This is the additional delay

the module will wait before

responding to a message

from the host. Increase

this value if you have

trouble communicating with

the module or you

encounter a high degree of

error messages.

0011 10

(000A)

Alternate

Method of

Module

Reset

Writing 41429 (A1D5H) to

this register will cause a

module reset. This is

provided as an alternate

method of Reset for

software that does not

support the Reset Slave

(08) command.

After a reset, this register

reads 0 (no reset).

This register is not

maintained in EEPROM.

41001

This block

mirrors

1xxxx

registers.

Refer to Note 3. 1xxxx

Discrete Input Registers

are mapped to the 41xxx

Holding Register space

using an address offset of

41000.

42001

This bl

ock

mirrors

0xxxx

registers.

Refer to Note 3. 0xxxx Coil

Registers are mapped to

the 42xxx Holding Register

space using an address

offset of 42000.

43001

This block

mirrors

3xxxx

registers.

Refer to Note 2. 3xxxx

Input registers are mapped

to the 43xxx Holding

address offset of 43000.

Notes (Register Map):

1. Configuration variables stored in holding registers (4xxxx

reference addresses) are maintained in EEPROM except as

noted. Changes to these register parameters do not take

effect until the next software or power-on reset of the

module.

Notes (Register Map)…continued:

2. For your convenience, this module mirrors the contents and

operation of 3xxxx registers into 43xxx holding register

space for systems and controllers that cannot directly

access 3xxxx registers. That is, the 3xxxx registers of this

model can be written to, or read from, using either the

standard methods described in the Modbus specification, or

through mapping (mirroring) to the Holding Register space.

The format of the registers are identical and you only need

to offset your address by 43000. For example: if you want to

read Input Register 1 through the Holding Registers, you

would use the “Read Holding Registers” function with an

address of 43001.

3. For modules with a firmware revision later than G (as in

9300-029G of 901MB, 9300-030G of 902MB, and 9300-

031G of 903MB), the mirroring function as described in Note

2 is augmented as follows (0xxxx also maps to 42xxx space,

and 1xxxx also maps to 41xxx space):

For 1xxxx Input Status Registers (where supported), the

return data is reformatted to match the Holding Register

format. For example, if you request Input Status for 12

digital inputs, instead of getting 2 bytes returned with the

first 12 bits representing 12 digital inputs, you will get 12

separate words (2 bytes) instead, with each set to 0000H

(OFF) or FFFFH (ON).

For 0xxxx Coil Registers (where supported), reads are

handled in the same way as noted for 1xxxx Input Status

Registers. That is, you may write to the coil registers using

the “Preset Single Register” function with an address offset

of 42000. Setting the data to 0000H will turn the coil OFF,

while setting the data to FF00H will turn the coil ON.

AN INTRODUCTION TO MODBUS

The Modbus protocol provides an industry standard method

that Series 900MB modules use for parsing messages. Modbus

devices communicate using a master-slave technique in which

only one device (the master) can initiate transactions (called

queries). The other devices (slaves) respond by supplying the

requested data to the master, or by taking the action requested in

the query. The Series 900MB modules are slaves, while a typical

master device is a host computer running appropriate application

software. Masters can address individual slaves, or can initiate a

broadcast message to all slaves. Slaves return a response to all

queries that are addressed to them individually, but no response

is returned to broadcast queries from a master device.

Remote Terminal Unit (RTU) Mode

The Series 900MB modules use the widely accepted Modbus

network protocol in the RTU (Remote Terminal Unit) serial

transmission mode. In RTU mode, each 8-bit message byte

contains two 4-bit hexadecimal characters, and the message is

transmitted in a continuous stream. The format for each byte in

RTU mode is outlined below:

RTU Mode Byte Format

Coding System 8-bit binary, hexadecimal 0-9, A-F, two

hexadecimal characters contained in each

8-bit field of the message.

Bits Per Byte 1 start bit + 8 data bits, lsb sent first + 1bit

for even/odd parity or no bit for no parity +

1 stop bit if parity is used, or 1 or 2 stop

bits with no parity.

Error Check Field Cyclical Redundancy Check (CRC)

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A master’s query is comprised of a slave address (or broadcast),

a function code defining the requested action, any data required,

and an error checking field. A slave’s response is comprised of

fields confirming the action taken, any data to be returned, and an

error checking field. The query and response both include a

device address + function code + data byte(s) + error checking

field. If an error occurred in the receipt of the query, or if the

slave is unable to perform the requested action, the slave will

return an exception message as its response (see Modbus

Exceptions). The error check field allows the master to confirm

that the message contents are valid.

Modbus Message Framing

A Modbus message is placed in a frame by the transmitting

device. A frame is used to mark the beginning and ending point

of a message allowing the receiving device to determine which

device is being addressed and to know when the message is

completed. It also allows partial messages to be detected and

errors flagged as a result.

RTU mode messages start with a silent interval of at least 3.5

character times implemented as a multiple of character times at

the baud rate being used on the network (indicated as t1t2t3t4

below). The first field transmitted is the device address. The

allowable characters transmitted for all fields are hexadecimal

values 0-9, A-F. A networked device continuously monitors the

network, including the silent intervals, and when the first field is

received (the address), the device decodes it to determine if it is

the addressed device. Following the last character transmitted, a

similar silent interval of 3.5 character times marks the end of the

message and a new message can begin after this interval. A

typical message frame is shown below.

RTU Message Frame

Start Addr. Function Data CRC End

t1t2t3t4 8 bits 8 bits nx8 bits 16 bits t1t2t3t4

The entire message must be transmitted as a continuous

stream. If a silent interval of more than 1.5 character times

occurs before completion of the frame, the receiving device

flushes the incomplete message and assumes the next byte will

be the address field of a new message.

In similar fashion, if a new message begins earlier than 3.5

character times following a previous message, the receiving

device assumes it is a continuation of the previous message.

This will generate an error, as the value in the final CRC field will

not be valid for the combined messages.

How Characters Are Transmitted Serially

When messages are transmitted on Modbus serial networks,

each character or byte is sent in order of Least Significant Bit

(LSB) to Most Significant Bit (MSB) as noted below (left to right):

RTU Character Framing (No Parity)

Start 0 1 2 3 4 5 6 7 Stop Stop

RTU Character Framing (With Parity)

Start 0 1 2 3 4 5 6 7 Parity Stop

Note that an additional stop bit is normally transmitted to fill

out the character frame for no parity. Acromag units will accept

one or two stop bits with no parity.

Modbus Addresses

The master device addresses a specific slave device by

placing the 8-bit slave address in the address field of the

message. Valid addresses are from 1-247. When the slave

responds, it places its own address in this field of its response to

let the master know which slave is responding. Address 0 is

reserved for the broadcast address, which all slave devices on a

network recognize. A slave does not issue a response to

broadcast messages. Further, not all function messages support

the broadcast address.

With respect to data addresses, all data addresses in

Modbus messages are referenced to 0, with the first occurrence

of a data item addressed as item number zero. Further, a

function code field already specifies which register group it is to

operate on (i.e. 0x, 1x, 3x, or 4x reference addresses). For

example, holding register 40001 is addressed as register 0000 in

the data address field of the message. The function code that

operates on this register specifies a “holding register” operation

and the “4xxxx” reference is implied. Holding register 40108 is

addressed as register 006BH (107 decimal).

Modbus Functions

The function code field of a message frame contains the 8

bits that tell the slave what kind of action to take. Valid codes are

in the range 1-255. Not all codes apply to a module and some

codes are reserved for future use. The following table highlights

the subset of standard Modbus functions supported by the Model

901MB/902MB/903MB modules (the reference register addresses

that the function operates on are also indicated):

CODE

FUNCTION

REFERENCE

01 (01H) Read Coil (Output) Status 0xxxx

02 (02H) Read Input Status 1xxxx

03 (03H) Read Holding Registers 4xxxx

04 (04H) Read Input Registers 3xxxx

05 (05H) Force Single Coil (Output) 0xxxx

06 (06H) Preset Single Register 4xxxx

08 (08H) Reset Slave

Hidden

15 (0FH) Force Multiple Coils (Outputs) 0xxxx

16 (10H) Preset Multiple Registers 4xxxx

17 (11H) Report Slave ID

Hidden

These functions are used to access the registers outlined in

the register map presented in the prior section for sending and

receiving data. Note that the Report Slave ID and Reset Slave

commands do not operate on register map registers.

When a slave device responds to the master, it uses the

function code field to indicate either a normal (error-free)

response, or that some kind of error has occurred (an exception

response). A normal response simply echoes the original

function code of the query, while an exception response returns a

code that is equivalent to the original function code with its most

significant bit (msb) set to a logic 1. For example, the Read

Holding Registers command has the function code 0000 0011

(03H). If the slave device takes the requested action without

error, it returns the same code in its response. But if an

exception occurs, it returns 1000 0011 (83H) in the function code

field and appends a unique code in the data field of the response

message that tells the master device what kind of error occurred,

or the reason for the exception (See Modbus Exceptions).

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The master’s application program must handle the exception

response. It may choose to post subsequent retries of the

original message, it may try sending diagnostic messages to the

slave, or it may simply notify the operator an exception error has

occurred.

The following paragraphs describe the Modbus functions

supported by Model 901MB/902MB/903MB modules. Note that

not all commands apply to each model. To gain a better

understanding of Modbus, please refer to the register map as you

review this material.

Read Coil Status (01)

(902MB & 903MB Models Only)

This command will read the ON/OFF status of discrete

outputs or coils (0x reference addresses) in the slave. For

902MB/903MB models, its response is equivalent to the gate

signal of the n-channel mosfet that drives the output. On 903MB

models which include tandem input channels, you can read the

corresponding input via the Read Input Status command to

determine the actual state of the drain via closed-loop feedback.

Broadcast transmission is not supported.

The Read Coil Status query specifies the starting coil (output

channel) and quantity of coils to be read. Coils correspond to the

discrete open-drain outputs and are addressed starting from 0

(up to 12 coils addressed as 0-11 for these models).

The Read Coil Status in the response message is packed as

one coil or channel per bit of the data field. The output status is

indicated as 1 for ON (sinking current), and 0 for OFF (not

conducting). The LSB of the first data byte corresponds to the

status of the coil addressed in the query. The other coils follow

sequentially, moving toward the high order end of the byte, and

from low order to high order in any subsequent byte. If the

returned coil quantity is not eight, the remaining bits of the data

byte will be set to zero toward the unused high order end of the

byte. The following example reads the output channel status of

coils 0-11 at slave device 247:

Read Coil Status Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 1 (01)

Starting Address High Order 0 (00)

Starting Address Low Order 0 (00)

Number Of Points High Order 0 (00)

Number Of Points Low Order 12 (0C)

Error Check (LRC or CRC) --

Note that the leading character of the 0x reference address is

implied by the function code and omitted from the address

specified. In this example, the first address is 00001 and

referenced via 0000H and this corresponds to coil 0.

Read Coil Status Example Response

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 1 (01)

Byte Count 2 (02)

Data (Coils 7-0) 170 (AA)

Data (Coils 11-08) 10 (0A)

Error Check (LRC or CRC) --

To summarize, the status of coils 7-0 is shown as the byte

value AA hex, or 10101010 binary. Coil 7 is the MSB of this byte,

and coil 0 is the LSB of this byte. Reading left to right, the output

status of coils 7..0 is ON-OFF-ON-OFF-ON-OFF-ON-OFF. This

is summarized as follows:

Bin 1 0 1 0 1 0 1 0

Hex A A

Coil 7 6 5 4 3 2 1 0

In the last (second) data byte, the status of coils 11..8 is

shown as the byte value 0A hex, or binary 0000 1010. Coil 11 is

the fifth bit position from the left and coil 08 is the LSB of this

byte. The four remaining bits (toward high-order end) are zero.

Bin 0 0 0 0 1 0 1 0

Hex 0 A

Coil NA NA NA NA 11 10 9 8

Read Input Status (02)

(901MB & 903MB Models Only)

This command will read the binary ON/OFF status of discrete

inputs (1x reference addresses) at the slave. On 903MB models

which have tandem input/output channels, you can read the

corresponding state of the output drain via closed-loop feedback

with this command. Broadcast transmission is not supported.

The Read Input Status query specifies the starting discrete

input channel and quantity of inputs to be read. Inputs are

addressed starting from 0 (up to 12 inputs addressed as 0-11).

Note that for 903MB models, and unlike the Read Coil Status

command, this command reflects the actual state of the output

drain, rather than the gate control signal that turns the output ON.

The Read Input Status in the response message is packed

as one input channel per bit of the data field. Inputs of these

models are asserted low. That is, the input status is indicated as

1 for ON (output sinking current or a low input signal), and 0 for

OFF (output not conducting or a high input signal). The LSB of

the first data byte corresponds to the status of the input

addressed in the query. The other coils follow sequentially,

moving toward the high order end of the byte, and from low order

to high order in any subsequent byte. If the returned coil quantity

is not eight, the remaining bits of the data byte will be set to zero

toward the unused high order end of the byte. The following

example reads the input channel status of digital inputs 0-11 at

slave device 247:

Read Input Status Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 2 (02)

Starting Address High Order 0 (00)

Starting Address Low Order 0 (00)

Number Of Points High Order 0 (00)

Number Of Points Low Order 12 (0C)

Error Check (LRC or CRC) --

Note that the leading character of the 1x reference address is

implied by the function code and omitted from the address

specified. In this example, the first address is 10001 and

referenced via 0000H and this corresponds to input channel 0.

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Read Input Status Example Response

Field Name

Example Value (H

ex)

Slave Address 247 (F7)

Function Code 2 (02)

Byte Count 2 (02)

Data (Coils 0-7) 170 (AA)

Data (Coils 11-8) 10 (0A)

Error Check (LRC or CRC) --

To summarize, the status of inputs 7-0 is shown as the byte

value AA hex, or 10101010 binary. Coil 7 is the MSB of this byte,

and coil 0 is the LSB of this byte. Reading left to right, the input

status of channels 7..0 is ON-OFF-ON-OFF-ON-OFF-ON-OFF, or

LO-HI-LO-HI-LO-HI-LO-HI if referring to actual input signal levels

(inputs of this model are asserted/ON low). In the last (second)

data byte, the status of channels 11..8 is shown as the byte value

0A hex, or binary 0000 1010. Channel 11 is the fifth bit position

from the left and channel 8 is the LSB of this byte. The four

remaining bits (toward the high-order end) are filled with zeros.

Read Holding Registers (03)

This command will read the binary contents of holding

registers (4x reference addresses) in the slave device. Broadcast

transmission is not supported.

The Read Holding Registers query specifies the starting

are addressed starting at 0 (registers 1-16 are addressed as 0-

15). The Read Holding Registers response message is packed

as two bytes per register, with the binary contents right-justified in

each byte. For each register, the first byte contains the high

order bits and the second byte the low order bits.

The following example reads holding registers 40001…40003

(slave address, baud rate, and parity) at slave device 247:

Read Holding Register Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 3 (03)

Starting Address High Order 0 (00)

Starting Address Low Order 0 (00)

Number Of Points High Order 0 (00)

Number Of Points Low Order 3 (03)

Error Check (LRC or CRC) --

Read Holding Register Example Response

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 3 (03)

Byte Count 6 (06)

Data High (Register 40001 0 (00)

Data Low (Register 40001) 247 (F7)

Data High (Register 40002) 0 (00)

Data Low (Register 40002) 2 (02)

Data High (Register 40003) 0 (00)

Data Low (Register 40003) 1 (01)

Error Check (LRC or CRC) --

To summarize, the contents of register 40001 (two bytes) is

slave address 247 (00F7H). The contents of register 40002 (two

bytes) is the baud rate setting 2 (9600bps). The contents of

Read Input Registers (04)

This command will read the binary contents of input registers

(3x reference addresses) in the slave device. Broadcast

transmission is not supported. The Read Input Registers query

specifies the starting register and quantity of registers to be read.

Note that registers are addressed starting at 0 (registers 1-16 are

addressed as 0-15). The Read Input Registers response

message is packed as two bytes per register, with the binary

contents right-justified in each byte. For each register, the first

byte contains the high order bits and the second byte the low

order bits.

The following example reads the module status register

30001 (flash checksum error flag, default mode flag, and port

watchdog timeout flags) at slave device 247:

Read Input Register Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 4 (04)

Starting Address High Order 0 (00)

Starting Address Low Order 0 (00)

Number Of Points High Order 0 (00)

Number Of Points Low Order 1 (01)

Error Check (LRC or CRC) --

Read Input Register Example Response

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 4 (04)

Byte Count 2 (02)

Data High (Register 30001) 0 (00)

Data Low (Register 30001) 0 (00)

Error Check (LRC or CRC) --

To summarize, the contents of register 30001 (two bytes)

indicates that no flags are set (0000H). That is, no checksum

error is present, the module is not in the default mode, and no

port timeouts have occurred.

Force Single Coil (05)

(902MB & 903MB Models Only)

This command will force a single coil/output (0x reference

address) ON or OFF. For broadcast transmission, this function

forces the same coil in all networked slaves. The Force Single

Coil query specifies the coil reference address to be forced, and

the state to force it to. The ON/OFF state is indicated via a

constant in the query data field. A value of FF00H forces the coil

to be turned ON (i.e. the gate of the corresponding n-channel

mosfet is set high), and 0000H forces the coil to be turned OFF

(i.e. the gate of the corresponding output mosfet is set low). All

other values are illegal and will not affect the coil. Note that coils

are referenced starting at 0—up to 12 coils are addressed as 0-

11 and this also corresponds to the output channel number. The

following example forces coil 9 ON (output 9) at slave device 247:

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Force Single Coil Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 5 (05)

Coil Address High Order 0 (00)

Coil Address Low Order 9 (09)

Force Data High Order 255 (FF)

Force Data Low Order 0 (00)

Error Check (LRC or CRC) --

Force Single Coil Example Response

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 5 (05)

Coil Address High Order 0 (00)

Coil Address Low Order 9 (09)

Force Data High Order 255 (FF)

Force Data Low Order 0 (00)

Error Check (LRC or CRC) --

The Force Single Coil response is an echo of the query as

shown above, returned after executing the force coil command.

No response is returned to broadcast queries from a master.

Preset Single Register (06)

This command will preset a single holding register (4x

reference address) to a specific value. Broadcast transmission is

supported by this command and will act to preset the same

The Preset Single Register query specifies the register

reference address to preset, and the preset value. Registers are

addressed starting at 0--registers 1-16 are addressed as 0-15.

The Preset Single Registers response message is an echo of the

query, returned after the register contents have been preset. The

following example writes a baud rate of 9600bps to holding

Preset Holding Register Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 6 (06)

Preset Data High Order 0 (00)

Preset Data Low Order 2 (02)

Error Check (LRC or CRC) --

Preset Holding Register Example Response

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 6 (06)

Preset Data High Order 0 (00)

Preset Data Low Order 2 (02)

Error Check (LRC or CRC) --

The response simply echoes the query after the register

contents have been preset. No response is returned to broadcast

queries from a master device.

Force Multiple Coils (15)

(902MB & 903MB Models Only)

This command will simultaneously force a sequence of coils

(0x reference addresses) either ON or OFF. Broadcast

transmission is supported by this command and will act to force

the same block of coils in all networked slaves.

The Force Multiple Coils query specifies the starting coil

reference address to be forced, the number of coils, and the force

data to be written in ascending order. The ON/OFF states are

specified by the contents in the query data field. A logic 1 in a bit

position of this field requests that the coil turn ON, while a logic 0

requests that the corresponding coil be turned OFF. Unused bits

in a data byte should be set to zero. Note that coils are

referenced starting at 0—up to 12 coils are addressed as 0-11

and this also corresponds to the output channel number.

The Force Multiple Coils normal response message returns

the slave address, function code, starting address, and the

number of coils forced, after executing the force instruction. Note

that it does not return the byte count or force value.

The following example forces odd-numbered coils (outputs)

OFF, and even numbered coils ON, for coils 0-11 at slave device

247:

Force Multiple Coils Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 15 (0F)

Coil Address High Order 0 (00)

Coil Address Low Order 0 (00)

Number Of Coils High Order 0 (00)

Number Of Coils Low Order 12 (0C)

Byte Count 02

Force Data High (First Byte) 170 (55)

Force Data Low (Second Byte) 5 (05)

Error Check (LRC or CRC) --

Note that the leading character of the 0x reference address is

implied by the function code and omitted from the address

specified. In this example, the first address is 00001,

corresponding to coil 0, and referenced via 0000H. Thus, the first

byte transmitted will address coils 7...0, with the least significant

bit addressing the lowest coil in this set as follows:

Bin 0 1 0 1 0 1 0 1

Hex 5 5

Coil 7 6 5 4 3 2 1 0

The second byte transmitted will address coils 11...8, with the

least significant bit addressing the lowest coil in this set as

follows (note that the four unused upper bits in the second data

byte are set to zero):

Bin 0 0 0 0 0 1 0 1

Hex 0 5

Coil NA NA NA NA 11 10 9 8

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Force Multiple Coils Example Response

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 15 (0F)

Coil Address High Order 0 (00)

Coil Address Low Order 0 (00)

Number Of Coils High Order 0 (00)

Number Of Coils Low Order 12 (0C)

Error Check (LRC or CRC) --

The normal response returns the slave address, function

code, starting coil address, and quantity of coils forced, after

executing the force instruction. It does not return the byte count

or force data. No response is returned to broadcast queries from

a master device.

Preset Multiple Registers (16)

This command will preset a block of holding registers (4x

reference addresses) to specific values. Broadcast transmission

is supported by this command and will act to preset the same

block of registers in all networked slaves.

The Preset Multiple Registers query specifies the starting

to be written in ascending order. Note that registers are

addressed starting at 0--registers 1-16 are addressed as 0-15.

The Preset Multiple Registers normal response message returns

the slave address, function code, starting register reference, and

the number of registers preset, after the register contents have

been preset. It does not echo the preset values.

The following example writes a new slave address of 200, a

baud rate of 28800bps, and sets parity to even, by writing to

holding registers 40001 through 40003 at slave device 247

(changes to slave address, baud rate, and parity will take effect

following a software or power-on reset of the module) :

Preset Multiple Registers Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 16 (10)

Starting Register High Order 0 (00)

Starting Register Low Order 0 (00)

Number Of Registers High Order 0 (00)

Number Of Registers Low Order 3 (03)

Byte Count 6 (06)

Preset Data High (First Register) 0 (00)

Preset Data Low (First Register) 200 (C8)

Preset Data High (Second Reg) 0 (00)

Preset Data Low (Second Reg) 5 (05)

Preset Data High (Third Reg) 0 (00)

Preset Data Low (Third Reg) 2 (02)

Error Check (LRC or CRC) --

Preset Multiple Registers Example Response

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 16 (10)

Starting Register High Order 0 (00)

Starting Register Low Order 0 (00)

Number Of Registers High Order 0 (00)

Number Of Registers Low Order 3 (03)

Error Check (LRC or CRC) --

The response simply echoes the query without returning the

preset values after the register contents have been preset. No

response is returned to broadcast queries from a master device.

Report Slave ID (17)

This command returns the model number, serial number, and

firmware number for the Acromag slave device, the status of the

Run indicator, and any other information specific to the device.

This command does not address Register Map registers.

Broadcast transmission is not supported.

The Report Slave ID query simply sends the slave address

and function code with error check (CRC or LRC) as follows:

Report Slave ID Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 17 (11)

Error Check (LRC or CRC) --

The Report Slave ID response message returns the slave

model ID and firmware number string as shown below:

Report Slave ID Example Response (Acromag)

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 17 (11)

Byte Count 26 (1A)

Acromag Slave ID

0 (00H) = 924MB-0900

1 (01H) = 913MB-0900

2 (02H) = 914MB-0900

3 (03H) = 917MB-0900

4 (04H) = 918MB-0900

5 (05H) = 901MB-0900

6 (06H) = 902MB-0900

7 (07H) = 903MB-0900

8 (08H) = 904MB-0900

9 (09H) = 905MB-0900

10 (0AH) = 906MB-0900

Run Indicator Status (ON)

255 (FF)

00=OFF, FF=ON

Firmware Number ASCII Byte

String (Additional Data Field)

“ACROMAG,9300-031A,

903MB-0900,”

(41 43 52 4F 4D 41 47 2C

39 33 30 30 2D 30 33 31

41 2C 39 30 33 4D 42 2D

30 39 30 30 2CH)

Serial Number ASCII Byte

String (Unique Per Module)

Six Numbers + Revision

“123456A”

(31 32 33 34 35 36 41H)

Error Check (LRC or CRC) --

Reset Slave (08)

This command is used to trigger a reset of the module and its

effect is equivalent to a power-on reset of the module. Note that

changes to baud rate, slave address, parity, and watchdog

registers are initiated following reset. The Reset Slave command

uses sub-function 01 (Restart Communications) of the standard

Modbus Diagnostics Command (08) to accomplish a module

reset. This function does not operate on register map registers.

Broadcast transmission is not supported.

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The Reset Slave query simply sends the slave address,

function code, sub-function code, and data (data is ignored and

simply echoed back), with error check (CRC LRC). A Reset

Slave response is simply an echoed acknowledge that is returned

just before the reset is executed. Allow a few seconds following

reset to reinitiate communication with a module.

Reset Slave Example Query

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 08 (08)

Sub-Function High Order Byte 0 (00)

Sub-Function Low Order Byte 1 (01)

Data Field High-Order Byte 0 (00)

Data Field Low Order Byte 0 (00)

Error Check (LRC or CRC) --

Reset Slave Example Response (Sent Prior To Reset)

Field Name

Example Value (Hex)

Slave Address 247 (F7)

Function Code 08 (08)

Sub-Function High Order Byte 0 (00)

Sub-Function Low Order Byte 1 (01)

Data Field High-Order Byte 0 (00)

Data Field Low Order Byte 0 (00)

Error Check (LRC or CRC) --

For Modbus software that does not support the Reset Slave

function, an alternate method of generating a module reset is

provided via a write to the Module Reset Register (See Reset

Module Register 40011 of Register Map).

Modbus Data Field

The data field of a message frame contains a multiple of 8

bits that provides the slave with any additional information the

slave requires to complete the action specified by the function

code. The data field typically includes register addresses, count

values, and written data. The data field can be nonexistent (zero

length) as not all messages require data.

If no error occurs, the data field of a response from a slave

will return the requested data. If an error occurs, the data field

returns an exception code (see Modbus Exceptions) that the

master application can use to determine the next action to take.

Supported Data Types

All I/O values are accessed via 16-bit Input Registers or 16-

bit Holding Registers (see Register Map). Input registers contain

information that is read-only. For example, the current input

value read from a channel, or the states of a group of digital

inputs. Holding registers contain read/write information that may

be configuration data or output data. For example, the high limit

value of an alarm function operating at an input, or an output

value for an output channel.

I/O values for 900MB models are represented by the

following simple data types for temperature, percentage, and

discrete on/off.

Summary Of Data Types Used By 900MB Modules

Data Types

Description

Count Value A 16-bit signed integer value representing

an A/D count, a DAC count, or a time value

with a range of –32768 to +32767.

Percentage A 16-bit signed integer value with resolution

of 0.005%/lsb. ±20000 is used to represent

±100%. For example, -100%, 0% and

+100% are represented by decimal values

–20000, 0, and 20000, respectively. The

full range is –163.84% (-32768 decimal) to

+163.835% (+32767 decimal).

Temperature A 16-bit signed integer value with resolution

of 0.1°C/lsb. For example, a value of

12059 is equivalent to 1205.9°C, a value of

–187 equals –18.7°C. The maximum

possible temperature range is –3276.8°C to

+3276.7°C.

Discrete A discrete value is generally indicated by a

single bit of a 16-bit word. The bit

number/position typically corresponds to

the discrete channel number for this model.

Unless otherwise defined for outputs, a 1

bit means the corresponding output is

closed or ON, a 0 bit means the output is

open or OFF. For inputs, a value of 1

means the input is in its high state (usually

>> 0V), while a value of 0 specifies the

input is in its low state (near 0V).

Modbus Error Checking Fields

Modbus networks employ two methods of error checking:

parity checking (even or odd parity, or none), and frame checking

(Cyclical Redundancy Check).

Parity Checking

A Modbus device can be configured for Even or Odd parity

checking, or for no parity checking, and this determines how the

parity bit of the data frame is set.

If even or odd parity checking is selected, the number of 1

bits in the data portion of each character frame is counted. Each

character in RTU mode contains 8 bits. The parity bit will then be

set to a 0 or a 1, to result in an even (Even parity), or odd (Odd

parity) total number of 1 bits. For example, if an RTU character

frame contains the following eight data bits: 1100 0011, then

since the total number of 1 bits is 4 (already an even number),

the frame’s parity bit will be 0 if even parity is selected. If odd

parity is used, then the parity bit will be set to 1, making the total

number of bits an odd number (five).

When a message is transmitted, the parity bit is calculated

and applied to the frame of each character transmitted. The

receiving device counts the quantity of 1 bits in the data portion of

the frame and sets an error flag if the count differs from that sent.

As such, parity checking can only detect an error if an odd

number of bits are picked up or dropped off from a character

frame during transmission. For example, if odd parity is

employed and two 1 bits are dropped from a character, the result

is still an odd count of 1 bits. Note that all devices on a Modbus

network must use the same parity. If no parity checking is

selected, then no parity bit is transmitted and no parity check is

made. An additional stop bit is transmitted to fill out the character

frame for the no parity selection.

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CRC Error Checking

RTU Mode message frames include an error checking

method that is based on a Cyclical Redundancy Check (CRC).

The error checking field of a frame contains a 16-bit value (two 8-

bit bytes) that contain the result of a Cyclical Redundancy Check

(CRC) calculation performed on the message contents.

The CRC value is calculated by the transmitting device and is

appended to the message as the last field in a message—the low

order byte is appended first, followed by the high-order byte.

Thus, the CRC high-order byte is the last byte to be sent in a

message. The receiving device calculates a CRC during receipt

of a message and compares the calculated value to that received

in the CRC field. If the two values differ, an error results.

The CRC is started by first preloading the 16-bit CRC register

to all 1’s. Successive 8-bit bytes of the message (only the 8-data

bits in each character—no start, stop, or parity bits) are applied to

the current contents of the register, and each 8-bit character is

exclusive OR’ed with the register contents. The exclusive OR

result is shifted in the direction of the least significant bit (lsb) of

the CRC, with a zero placed into the most significant bit (msb).

The lsb is then extracted and examined, if the lsb is a 1, the

a 0, no exclusive OR takes place. This process is repeated until

8 shifts have been performed. After the last (eighth) shift, the

next 8-bit byte is exclusive OR’ed with the register’s current

contents, and the process repeats itself for 8 more shifts as

described above. The final contents of the CRC register after all

the message bytes have been applied is the CRC value.

Modbus Exceptions

If an unsupported function code is sent to a module, then the

exception code 01 (Illegal Function) will be returned in the data

field of the response message. If a holding register is written with

an invalid value, then exception code 03 (Illegal Data Value) will

be returned in the response message. The following table lists

possible exception codes:

Modbus Exception Codes

Code

Exception

Description

01 Illegal Function The function code received in the

query is not allowed or invalid.

02 Illegal Data

Address

The data address received in the

query is not an allowable address

for the slave or is invalid.

03 Illegal Data

Value

A value contained in the query

data field is not an allowable value

for the slave or is invalid.

04 Slave Device

Failure

An unrecoverable error occurred

while the slave was attempting to

perform the requested action.

05 Acknowledge The slave has accepted the

request and is processing it, but a

long duration of time is required to

do so. This response is returned

to prevent a timeout error from

occurring in the master.

06 Slave Device

Busy

The slave is engaged in

processing a long-duration

program command. The master

should retransmit the message

later when the slave is free.

Modbus Exception Codes…continued

ode

Exception

Description

07 Negative

Acknowledge

The slave cannot perform the

program function received in the

query. This code is returned for

an unsuccessful programming

request using function code 13 or

14 (code not supported by this

model). The master should

request diagnostic information

from the slave.

08 Memory Parity

Error

The slave attempted to read

extended memory, but detected a

parity error in memory. The

master can retry the request, but

service may be required at the

slave device.

In a normal response, the slave echoes the function code of

the original query in the function field of the response. All

function codes have their most-significant bit (msb) set to 0 (their

values are below 80H). In an exception response, the slave sets

the msb of the function code to 1 in the returned response (i.e.

exactly 80H higher than normal) and returns the exception code

in the data field. This is used by the master’s application to

recognize an exception response and examine the data field for

the exception code.

MODULE SOFTWARE CONFIGURATION

From the factory, each module has a default configuration as

detailed in the INSTALLATION section of this manual. Your

application will likely differ from the default configuration and the

module will need to be reconfigured. Series 900MB modules

may be configured by issuing the appropriate Modbus functions

to the Register Map registers, as required to configure the unit.

However, it is much simpler to use the 900MB Configuration

Software to program and control the module parameters and

operating modes. This software is easy to use, self-explanatory,

and complete configuration takes only a few minutes. On-line

help is built-in. As such, a comprehensive guide to the use of this

program is not necessary. To begin configuration, you should

already be familiar with Windows operation and have a basic

understanding of module terminology as it relates to your model.

Before You Begin

1. Have you installed the 900MB Configuration Program? You

should complete the MODULE INSTALLATION (Section 2.0)

of this manual before proceeding.

2. Check that all necessary electrical connections have been

made and that power is applied (module’s green LED ON).

3. Have you set the correct baud rate at the RS485 converter

(or repeater if used)?

4. Have you tried communicating using the Default Mode?

Press the “DFT” push-button of the module until the yellow

status LED is flashing. This sets the module’s

communication parameters to 9600 baud, a slave address

of 247, no parity, and one or two stop bits.

5. If you fail to communicate with the module or have a high

degree of communication errors, try increasing the response

delay time (See Response Delay Register 40010). Some

network converters or host/software systems cannot accept

an immediate response from a slave device without the

additional delay provided via this parameter.

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The following sections guide you

through the Configuration Program

property sheets used to configure

90xMB I/O Modules. Because these

units perform simple digital I/O,

configuration is simplified. Property

sheets vary slightly between models.

Refer to on-line Help if you have trouble

understanding parameters unique to

your module.

Starting The Program

After clicking on the Series 900MB

program icon to boot the Configuration

Program, a screen will be displayed

similar to that shown at right.

To begin, click on the “Settings-Serial

Communications…” pull-down menu (or

press Ctrl-E) to set the COM port, baud

rate, parity, and slave address that the

host computer will use to communicate

with the module. Optionally, you can

check the “Update Communications

settings at download” box to

automatically change the host settings

to match the module if new settings are

later downloaded to the module

(recommended to conveniently maintain

communication with a module following

reconfiguration).

↑↑

Available menu selections are listed below. COM Port MODULE

Note that the host COM port

selected is indicated in the first

box of the lower right-hand

corner. MODULE is indicated in

the third box if a connected

module is detected by the

software. The fourth and fifth

boxes indicate NUM for Num lock

and CAP for Caps lock,

respectively.

File

New…

Open…

Save

Save As…

Print…

Print Preview

Print Setup…

Recent File Indicated

Exit

Use File-New to create a new

configuration file. You will be

prompted to select a model

number. Use File-Open to open

an existing configuration file.

Use File-Save to save the

current configuration file to disk.

Use File-Save As to save the

current configuration file to a new

file name.

Use File-Print to get a printout of

the currently loaded configuration

file. Use File-Print Preview to

view the current configuration or

preview the print documentation.

Use File-Print Setup to select a

printer and font style.

Module

Upload Configuration

Download Configuration

Use Module-Upload

Configuration to upload the

module’s current configuration

and calibration. Use Module-

Download Configuration to

write the currently loaded

configuration to the module.

Settings-

Serial Communications…

Communications Port

Host Baud Rate

Host Parity

Slave Address

Use the Communications Port

scroll window to select the host

COM port the module is

connected to (COM1-COM4), or

type in a COM port as required,

from COM1 to COM99.

The selected COM port is

indicated in the lower right hand

corner of the screen.

Use the Baud Rate scroll window

to select the baud rate to be used

by the host in communicating

with the module.

Use the Parity scroll window to

select Odd, Even, or No Parity

checking by the software for data

transfer.

Use the Slave Address scroll

window to tell the software which

module to address.

If you wish to maintain

communications with a module

following download, check the

“Update Communications

settings at download” box of

the Settings window to keep the

host in synch with a module if the

module settings are changed.

If the module is in Default Mode

(indicated via a flashing status

LED), the baud rate, address, &

parity assumed by the module

are fixed at 9600bps, 247, & No

Parity. You must use the same

settings as the connected

module.

Help

Configuration Help Topics

Your Model Help Topics

About Modbus Configuration

About Your Model

Use Help to obtain information

about using this software or

configuring transmitters. Note

that context sensitive help (↑?) is

also available for help on a

specific field or topic. Simply

click on the [↑?] button, then click

on the field or topic of interest to

obtain help on that subject. You

may also click the right mouse

button to copy or print the help

screen while it is being displayed.

The following sections review the

configuration of a Model

903MB-0900 transmitter module.

Configuration of your model will

be similar.

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Creating A Configuration File

You may use File-New to create a new

configuration file, or File-Open to open

an existing configuration file. You may

also use Module-Upload

Configuration to retrieve the current

active configuration from the module

connected (recommended).

Uploading first is recommended as it will

automatically detect the correct model

connected and load the property sheets

for that model.

Once you create, open, or upload a

configuration file, a screen similar to the

one shown at right will be displayed.

The model number is indicated at the

top of the screen along with the current

file name. Model 903MB Configuration

is shown here. Your screen will vary

according to your model number.

Note that only 2 property sheets define

this transmitter’s configuration: General

and Test.

↑

Module Present

Module

The Serial and Firmware numbers are

indicated at the top of the General screen

and cannot be modified.

For “Tag:”, enter up to 15 alphanumeric

characters (optional).

For “Comment:”, enter up to 31

alphanumeric characters (optional).

For “Configured By:”, enter your name up

to 15 alphanumeric characters (optional).

You can also add a “Location:” note of up

to 25 alphanumeric characters (optional).

For “ID Port:”, enter up to 15 alphanumeric

characters of identification information

relative to the port (optional).

Use the “Slave Address” scroll bar to

select a new module address that will take

effect following download. Select from 1 to

247. Address 247 is reserved for Default

Mode.

Use the “Baud Rate” scroll bar to select a

new baud rate to be used by the module

following download. Select 2400, 4800,

9600 (Default Mode), 14400, 19200,

28800, 38400, 57600, 76800, or 115200

bits per second.

Use the “Parity” scroll bar to select Odd,

Even, or No Parity (Default Mode) error

checking by the module.

Use the “Response Delay” field to specify

a delay from 0 to 65500 ticks with 1 tick

equal to 1.085 micro-seconds. Response

delay is the additional turnaround delay

applied between message receipt by the

module and its response to the host. A

fixed amount of delay is already present

and varies with the model. Thus, you will

have to specify a comparable amount of

response delay to measure any affect.

Some host software or signal converters

require additional delay to work properly.

Note that slave address, baud rate, parity,

and response delay selections take effect

following the next module reset and do not

alter the settings used by the host software

(which are configured separately via the

Settings menu).

If you checked the “Update

Communications settings at download” box

of the Settings pull-down menu, the host

software will automatically change its own

settings to match the module settings that

take effect following download in an effort

to easily maintain communication with the

module. Otherwise, you must change the

host settings separately after downloading

to match the new module settings.

If the module is in Default Mode (indicated

via a flashing status LED), the baud rate,

address, and parity of the module are fixed

at 9600bps, 247, and No Parity.

The Test Screen of the next page also

provides configuration information with

respect to the port watchdog timers and

output timeout states.

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Testing Your Configuration

The “Test” portion of this program

allows you to monitor polling, module

status flags, reset the module, control

output states, and monitor input states.

This page is also used to configure the

port watchdog time and the timeout

reset states for the port.

Port I/O Watchdog Timer

The right half of this screen allows you

to configure the Port I/O Watchdog

Timer. A watchdog timeout is triggered

if no channel read or write occurs for

one or more port channels, within the

timeout period specified. A timeout is

cleared and the timer reinitiated when a

port channel read or write occurs. Note

that clearing a timeout does not return

the outputs to their pre-timeout state.

They will retain their current state until

otherwise written.

Use the port 0, 1, & 2 “Timeout

Output” scroll bar to select the timeout

binary pattern to program the port

outputs to following a timeout. A pattern

of four bits is selected via this scroll bar

and represents the ON (1) and OFF (0)

states the port output channels are to

be sent to following a watchdog timeout.

The lsb corresponds to the lowest

numbered port channel. Select “None”

if you want the port outputs to remain in

their current states upon timeout.

Use the port 0, 1, & 2 “Watchdog

Time” field to specify a watchdog

timeout period up to 65534 seconds

(18.2 hours). A value of 0 or 65535 will

disable the port watchdog function and

“Disabled” will be indicated below the

Watchdog Time field.

Note that when this screen is selected,

the module channels are continuously

polled. Thus, you are not likely to ever

encounter a watchdog timeout with this

screen displayed.

Testing Your Operation

This screen also allows you to monitor

polling, module status flags, reset the

module, control output states, and

monitor input states.

For each I/O channel, the current true

input state is reflected via the simulated

LED’s of the module graphics. These

LED’s match the LED’s on the front of

the module.

For 903MB models, input buffers are

connected in tandem with open-drain

outputs for convenient loopback

monitoring of the output state. The

source leads of each port output

channel are tied in common to the port

return lead (RTN). The drain leads are

pulled up to the port excitation terminal

via resistor SIP’s installed in sockets at

each port. An external excitation supply

must be connected between the port

EXC and RTN terminals. Turning an

output ON connects the I/O lead to

return via the output mosfet. The inputs

are active-low, as the outputs are open-

drain, low-side switches. The 901MB &

902MB are the same as the 903MB, but

the 901MB has outputs removed and

the 902MB has inputs removed.

The output state of each port output

channel is set via the “ON” or “OFF”

bullet (902MB & 903MB units only).

Simply click ON or OFF as desired to

turn the corresponding output ON or

OFF. The output state corresponds to

the gate signal of the output channel’s

mosfet and may not reflect the actual

state of the mosfet’s source lead if the

drain is left open or floating. The actual

output state of the 906MB is obtained

via the simulated module LED’s, as the

input buffer is tied directly to the drain of

the output mosfet which connects to the

output terminal. Thus, for 903B models,

the input state reflects the actual state

of the open-drain output for the tandem

I/O channel via closed-loop feedback.

However, on 902MB models, input

circuitry is removed and the input state

is assumed equivalent to the output

state as it reflects the gate signal of the

corresponding output mosfet. Thus, the

902MB LED’s are driven via the gate

signal and not the actual output signal.

Print Your Configuration

If you wish to document your transmitter

configuration, then select File-Print to

get a two page printout of all of your

selected configuration parameters.

Saving Your Configuration

Note that the currently loaded

configuration file name is indicated at

the top of the screen to the right of the

model number.

You may select File-Save As to save

your configuration file to disk and give it

a new file name. Otherwise, use File-

Save to save the current file without

renaming it.

In the event that you lose a

configuration file, you can always

upload it from the module via Module-

Upload Configuration.

Note that the configuration process will

vary slightly for other model types.

Now wasn’t that easy! That’s all there is

to using the Configuration software to

configure your module. The module is

now ready for installation in the field.

BusWorksModel 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O

___________________________________________________________________________________________

- 19 -

4.0 THEORY OF OPERATION

Refer to Simplified Schematic 4501-809 and Functional Block

Diagram 4501-810 to gain a better understanding of the circuit.

Note that these modules will interface with any mix of up to

twelve digital input or output signals according to the model, and

provide network commands to configure the module, monitor the

inputs, and control the outputs. The outputs are the open-drains

of n-channel mosfets. Input buffers are connected in tandem with

the drain circuits via series 100KΩresistors. Over-voltage

clamps to +5V are connected to the buffer inputs. I/O terminals

also include transient suppression. Sockets are installed for

installation of optional input or output drain pullup resistors.

These resistors are pulled up to an external supply connected to

the EXC+ and RTN terminals. The microcontroller completes the

information transfer according to the I/O type and its embedded

program. I/O lines of the microcontroller switch the outputs

ON/OFF, and sample the digital inputs, as required. The UART

of the microcontroller sends/receives its I/O signals to the

network via an optically isolated RS485 transceiver. Embedded

configuration parameters are stored in non-volatile memory

integrated within the micro-controller. Only the functions required

by an application are actually stored in memory—new

functionality can be downloaded via the host running the Modbus

Configuration Software, or other compatible Modbus software

along the network. A wide input switching regulator (isolated

flyback) provides isolated power to the I/O circuit and RS485 port.

Refer to Functional Block Diagram 4501-810 for an overview of

how the software configuration variables are arranged.

5.0 SERVICE AND REPAIR

CAUTION:

Risk of Electric Shock - More than one

disconnect switch may be required to de-energize the

equipment before servicing.

SERVICE AND REPAIR ASSISTANCE

This module contains solid-state components and requires no

maintenance, except for periodic cleaning and transmitter

configuration parameter verification. Since Surface Mounted

Technology (SMT) boards are generally difficult to repair, it is

highly recommended that a non-functioning module be returned

to Acromag for repair. The board can be damaged unless special

SMT repair and service tools are used. Further, Acromag has

automated test equipment that thoroughly checks and calibrates

the performance of each module. Please refer to Acromag’s

Service Policy Bulletin or contact Acromag for complete details

on how to obtain service parts and repair.

PRELIMINARY SERVICE PROCEDURE

Before beginning repair, be sure that all installation and

configuration procedures have been followed. Make sure that the

correct baud rate is selected for the RS232-to-RS485 converter

employed The unit routinely performs internal diagnostics

following power-up or reset. During this period the green “Run”

LED flashes. If the diagnostics complete successfully, the “Run”

LED will stop flashing after two seconds and remain ON. This

indicates that the unit is operating normally. If the “Run” LED

continues to flash, then this is indicative of a problem. In this

case, use the Acromag Modbus Configuration Software to

reconfigure the module and this will usually cure the problem. If

the diagnostics continue to indicate a problem (a continuously

flashing green LED), or if other evidence points to a problem with

the unit, an effective and convenient fault diagnosis method is to

exchange the questionable module with a known good unit.

Acromag’s Application Engineers can provide further

technical assistance if required. When needed, complete repair

services are available from Acromag.

TROUBLESHOOTING

If you fail to communicate with the Model 903MB…

1. Is power ON at the module and the RS485 signal converter

(Green power LED continuously ON)?

2. Have you set the correct baud rate at the RS485 converter

(and/or repeater if used)? Is your host set to the proper

baud rate and parity? Are you using the correct address?

3. Have you tried communicating using the Default

Communication Mode? Press the “DFT” push-button of the

903MB module until the yellow status LED is flashing. This

sets the module’s communication parameters to 9600 baud,

a slave address of 247, no parity, and two stop bits. Be sure

to also set the baud rate of your RS485 converter and/or

repeater to 9600 baud.

4. Has the module been reset? The module will automatically

leave the Default Communication Mode following a software

or power-on reset and new settings for address, baud rate,

and parity will take effect following reset. If the yellow status

LED is not blinking or OFF, the module is no longer in the

Default Mode. Be sure to make host/software adjustments

to the baud, parity, and address parameters following a

reset of the module, as required to maintain communication.

5. If you fail to communicate with the module or have a high

degree of communication errors, try increasing the response

delay time (See Response Delay Register 40010). Some

network converters or host/software systems cannot accept

an immediate response from a slave device without

additional delay inserted between message receipt and

module response.

BusWorksModel 903MB/902MB/901MB Network I/O Module User’s Manual Digital I/O

___________________________________________________________________________________________

- 20 -

6.0 SPECIFICATIONS

General: Series 901/902/903MB network modules include up

to twelve digital inputs (901MB), digital outputs (902MB), or

combined input and output channels (903MB), and provide an

isolated RS485/Modbus network interface. Outputs are

open-drain, low-side switches and inputs are active-low.

Isolation is supplied between channel I/O, the network, and

power. The high-voltage, high-current outputs provide

discrete on/off control of external devices, while the non-

inverting, buffered inputs provide support for digital level

sensing or for simple readback of the outputs (903MB).

Inputs and outputs share common. Socketed I/O pullup

resistors are tied to the EXC+ terminal. This network module

is DIN-rail mounted.

The unit is configured and controlled with our user-friendly

Windows 95/98or NT900MB Configuration Program.

Optionally, you may use your own software as long as you

adhere to the Modbus command/response format for

supported commands. A push button on the module allows

communication with a module when its address, baud rate,

and parity settings are unknown. Non-volatile

reprogrammable memory in the module stores configuration

information.

MODEL NUMBER DEFINITION

Transmitters are color coded with a white label. The prefix

“9” denotes the Series 900, while the “MB” suffix specifies that

this device is primarily a process transmitter for Modbus

networks.

901MB: Transmits and isolates up to 12 digital input channels.

902MB: Transmits and isolates up to 12 digital output channels.

903MB: Transmits and isolates up to 12 digital I/O channels.

-0900: The four digits of this model suffix represent the

following options, respectively:

0 = No Options;

9 = Output: RS485/Modbus;

0 = Enclosure: DIN rail mount;

0 = Approvals: CE, UL, and cUL Listed.

I/O SPECIFICATIONS

Input and output circuits are connected in tandem to an I/O

terminal of the fully populated 903MB models. The same circuit

board is used to build all three models. Input circuitry is removed

for 902MB models (output only), and output circuitry is removed

for 901MB models (input only). Supported outputs are the open

drains of n-channel mosfets and intended for low-side switching

applications. Input buffers include series 100KΩbuffer resistors,

plus diode over-voltage clamps to +5V, and are active-low.

Transient protection is provided at each I/O terminal. Sockets for

installation of optional pullup resistor SIP’s are also provided. A

5.6K pullup resistor SIP is installed from the factory. The unit

must be properly wired and configured for the intended I/O type

(see Installation Section for details). Outputs may also be read

back via the corresponding input (903MB). The unit is easily

configured via the Modbus Configuration Program.

The following paragraphs summarize this model’s I/O types

and applicable specifications.

Digital Inputs (901MB & 903MB): Supports up to 12 active-low,

buffered inputs, with a common connection (RTN). For DC

voltage applications only. Observe proper polarity.

Inputs include transient suppression devices and series

connected 100KΩresistors, plus diode over-voltage clamps

to the internal +5V supply. Sockets are provided for

installation of optional SIP resistor networks to act as pullups

to the EXC+ terminal for the port. 5.6K pullup resistors are

installed from the factory. An excitation supply is typically

connected between the EXC+ and RTN terminals of the port.

Input Signal Voltage Range: 0 to +35VDC.

Input Current: 293uA, typical at 35VDC. This is computed

as the applied input voltage minus 5.7V, divided by the series

100KΩinput resistance.

Input Signal Threshold: TTL compatible with 100mV of

hysteresis, typical. Low-to-High threshold is 1.7VDC typical,

High-to-Low threshold is 1.6VDC, typical. Limit logic

transition to TTL levels of 0.8VDC (Max LOW level) and

2.0VDC (Min HIGH level).

Input Resistance: 100KΩ, typical.

Input Hysteresis: 100mVDC typical.

Input Response Time: 800ns typical, input transition to

logic level at microcontroller. The microcontroller then

samples the inputs (as a group) approximately every 650us.

The actual input sampling rate will vary as interrupts may

occur.

Digital Outputs (902MB & 903MB Only): Up to 12 independent,

open-drain, DMOS mosfet switches with a common source

connection at the port terminals labeled RTN. Channels are

grouped 4 to a port and include socketed pullup resistor SIP’s

to the port EXC+ terminal. A 5.6K pullup SIP resistor is

installed from the factory at each port. Outputs are for DC

voltage and current-sinking applications only, observe proper

polarity. To control higher voltages and/or currents, or for

controlling AC, an interposing relay may be used (see

Electrical Connections Drawing 4501-813). Transient

protection is built-in, but additional external protection is

recommended when switching inductive loads (see Drawing

4501-813). Note: When the outputs are used to control

interposing relays for switching AC and DC devices of higher

voltage/current levels, the coil ratings for the interposing relay

shall not exceed 24VDC, 100mA.

Output “OFF” Voltage Range: 0 to 35V DC. Limit voltage

to 35V or less or damage to the unit may result.

Output “OFF” Leakage Current: :0.1uA typical, 50uA

maximum (mosfet only, 25°C, 35V). Does not include the

tandem input bias current of 903MB models (see below).

Note (903MB): The 100KΩseries input buffer resistors in

combination with the +5V voltage clamps at the input buffers

will tend to increase the off-state drain current with increased

drain voltage (up to 0.3mA at 35V). This is due to the fact

that the input buffer circuitry and output mosfet drain circuitry

are connected in tandem to the same I/O pin for the Model

903MB.

Output “ON” Current Range: 0 to 500mA DC, continuous

(up to 6A total for all 12 channels combined). No deration

required at elevated ambients. Group one RTN per each

group of 4 outputs.

Output R

ON Resistance: 0.13Ωtypical, 0.28Ω

Maximum.

Output Response Time: An output is updated within 250us

of receipt of a Force Single Coil command. For Force

Multiple Coils command, the first coil will update in about

250us, followed successively by each additional coil every

180us. For 903MB units, the output logic transition to input

logic level time is 3us typical. Actual switching time will vary

with output load and interrupts.

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