ABB DATUM L150 User manual

ABB Instrumentation
DATUM L150/160 Operating Guide
MODBUS (RTU)
Communications Option
DATUML150
888888
A1
A2
A3
888888
DATUML160

Note.
Clarification of an instruction or
additional information.
Information.
Further reference for more detailed
information or technical details.
Use of Instructions
Although Warning hazards are related to personal injury, and Caution hazards are
associated with equipment or property damage, it must be understood that operation of
damaged equipment could, under certain operational conditions, result in degraded
process system performance leading to personal injury or death. Therefore, comply fully
with all Warning and Caution notices.
Informationinthismanualisintendedonlytoassistourcustomersintheefficientoperation
of our equipment. Use of this manual for any other purpose is specifically prohibited and
its contents are not to be reproduced in full or part without prior approval of Technical
Communications Department, ABB Instrumentation.
Health and Safety
To ensure that our products are safe and without risk to health, the following points
must be noted:
1. The relevant sections of these instructions must be read carefully before
proceeding.
2. Warning labels on containers and packages must be observed.
3. Installation, operation, maintenance and servicing must only be carried out by
suitably trained personnel and in accordance with the information given.
4. Normal safety precautions must be taken to avoid the possibility of an accident
occurring when operating in conditions of high pressure and/or temperature.
5. Chemicalsmustbestoredawayfromheat,protectedfromtemperatureextremes
and powders kept dry. Normal safe handling procedures must be used.
6. When disposing of chemicals ensure that no two chemicals are mixed.
Safety advice concerning the use of the equipment described in this manual or any
relevant hazard data sheets (where applicable) may be obtained from the Company
address on the back cover, together with servicing and spares information.
Warning.
An instruction that draws attention to
the risk of injury or death.
Caution.
An instruction that draws attention to
the risk of damage to the product,
process or surroundings.

1
CONTENTS
1 INTRODUCTION ........................................................................................... 2
2 ELECTRICAL INSTALLATION .................................................................... 3
2.1 Host Computer Serial Communications............................................... 3
2.2 OPTO22 Boards for use with Personal Computers............................. 3
2.3 Two-wire and Four-wire Connection .................................................... 3
2.4 Pull-up and Pull-down Resistors .......................................................... 6
2.5 Termination Resistor ............................................................................ 6
2.6 Serial Connections ............................................................................... 6
3 CONFIGURATION ........................................................................................ 8
3.1 Accessing the Configuration Mode ...................................................... 8
3.2 Setting the Serial Transmission Parameters ....................................... 8
3.3 Setting the MODBUS Address ............................................................. 8
4 MODBUS PROTOCOL ................................................................................. 9
4.1 Introduction ........................................................................................... 9
4.2 MODBUS Function Codes.................................................................. 10
5 MODBUS FUNCTIONS............................................................................... 11
5.1 Read Coil Status – Function Code 01 ............................................... 11
5.2 Read Holding Register – Function Code 03 ...................................... 12
5.3 Force Single Coil – Function Code 05 ............................................... 13
5.4 Preset Single Register – Function Code 06 ...................................... 14
5.5 Loopback Test – Function Code 08 ................................................... 15
5.6 Write Multiple Registers – Function Code 16 .................................... 16
6 EXCEPTION RESPONSES ........................................................................ 17
6.1 Examples ............................................................................................ 17
7 ADDRESSABLE PARAMETERS............................................................... 18
7.1 Coils ............................................................................................... 18
7.2 Registers ............................................................................................. 18
7.2.1 Analog Inputs ........................................................................ 18
7.2.2 Alarm Settings....................................................................... 19
7.2.3 Maths Functions.................................................................... 19

2
1 INTRODUCTION
This Operating Guide describes the DATUM L150/L160 MODBUS serial data
communications option and must be used in conjunction with the standard
User
Guide
( IM/L150 or IM/L160 ) supplied with the instrument.
Information.
The MODBUS option provides the following facilities:
• Standard RS422/485 communications.
• MODBUS RTU protocol – for master (host computer) to slave
(DATUM L150/L160) system.
• 500V d.c. isolation from external connections to the instrument.
• Two-wire or four-wire communication.
• 2400 or 9600 baud transmission rate.
• Parity-checking – odd, even or none.

3
2 ELECTRICAL INSTALLATION
This section describes the connection of serial data transmission cables between
the master (host computer) and slave DATUM L150/L160 instruments on a
MODBUS serial link. All connections other than those used for serial
communication are shown in Section 5 of the relevant
User Guide .
2.1 Host Computer Serial Communications
An RS422/485 communications driver must be fitted to the host computer. It is
strongly recommended that the interface has galvanic isolation to protect the
computer from lightning damage and increase signal immunity to noise pick-up.
2.2 OPTO22 Boards for use with Personal Computers
Where a personal computer is used as the host computer, the following OPTO22
boards are recommended for use with the DATUM L150/L160 Series of
instruments:
Part No. Computer Type
AC24 AT AT Bus IBM PC compatible
AC34 Microchannel IBM PC
2.3 Two-wire and Four-wire Connection – Figs. 2.1 and 2.2
MODBUSserialcommunicationsmustbeconfigured as either two-wire or four-wire
seriallinks – seeFigs. 2.1 and2.2. Two-/Four-wire operationmust also beselected
in the Configuration Mode – see Section 3.1.

4
…2 ELECTRICAL INSTALLATION
2.4 Pull-up and Pull-down Resistors – Figs. 2.1 and 2.2
To prevent false triggering of slaves when the master (host computer) is inactive,
pull-upandpull-down resistors must be fittedtotheRS422/485interface in the host
computer – see Figs. 2.1 and 2.2.
+5V
0V
1.8kΩPull-up
Resistor
1.8kΩPull-down
Resistor
Host Computer
Rx–
Rx+
Tx–
Tx+
'A'
'A
'B'
'B
GND
20
21
22
23
24
Tx+/Rx+
Tx–/Rx–
GND
+5V
0V
1.8kΩPull-up
Resistor
1.8kΩPull-down
Resistor
Host Computer
Rx–
Rx+
Tx–
Tx+
'A'
'A
'B'
'B
GND
Tx+/Rx+
Tx–/Rx–
GND
11 12 13
Fig. 2.1b Two-wire Operation – L160
Fig. 2.1a Two-wire Operation – L150

5
2 ELECTRICAL INSTALLATION…
…2.4 Pull-up and Pull-down Resistors
Host Computer
+5V
0V
'A 'B
1.8kΩ
Pull-down
Resistor
1.8kΩPull-up
Resistor
0V
+5V
0V
'A
'B
1.8kΩ
Pull-down Resistor
1.8kΩ
Pull-up
Resistor
Rx+
Rx–
Tx–
Tx+
GND
20
21
22
23
24
Fig. 2.2a Four-wire Operation – L150
Fig. 2.2b Four-wire Operation – L160
Host Computer
+5V
0V
'A 'B
1.8kΩ
Pull-down
Resistor
1.8kΩPull-up
Resistor
0V
+5V
0V
'A
'B
1.8kΩ
Pull-down Resistor
1.8kΩ
Pull-up
Resistor
Rx+
Rx–
Tx–
Tx+
GND
9 10 11 12 13

6
…2 ELECTRICAL INSTALLATION
2.5 Termination Resistor – Fig. 2.3
For long transmission lines, a 120Ωtermination resistor must be fitted to the last
slave in the chain – see Fig. 2.3.
First
S
lave Last
S
lave
Tx+
Tx-
Rx+
Rx-
GND
120Ω
Termination Resistor
(External)
M
as
t
er
Rx+
Rx–
Tx+
Tx–
GND
Tx+
Tx–
Rx+
Rx–
GND
Host
Computer
Fig. 2.3 Connecting Multiple Slaves
2.6 Serial Connections – Figs. 2.1 to 2.4
Information.
• Up to 10 slaves can be connected to a single RS422 adaptor card on a PC.
• Up to 32 slaves can be connected to a single RS485 adaptor card on a PC.
The number of slaves can be increased if the driver's serial port permits.
Connections to the MODBUS serial board must be made as shown in Figs. 2.1, 2.2
or 2.4. Connections on links with multiple slaves must be made in parallel, as
shown in Fig. 2.3. When connecting cable screens, ensure that no 'ground loops'
are introduced.
Themaximum serial datatransmission line length forboth RS422 and RS485 systems is
1200m. The types of cable that can be used are determined by the total line length:
Up to 6m – standard screened or twisted pair cable.
Up to 300m – twin twisted pair with overall foil screen and an integral drain
wire, e.g. Belden 9502 or equivalent.
Up to 1200m – twin twisted pair with separate foil screens and integral drain
wires, e.g. Belden 9729 or equivalent.

7
2 ELECTRICAL INSTALLATION
…2.6 Serial Connections – Figs. 2.1 to 2.4
Rx+
Rx–
Tx+
GND
Rx+
Rx–
Tx+
Tx–
GND
OPTO22 Adaptor
Board Connections
Screen
Tx– 8
9
4
5
3
Fig. 2.4 OPTO22 Board Connections

8
3 CONFIGURATION
Fig. 3.1 Setting Serial Transmission Parameters
Information.
• Programmable baud rate – 2400 or 9600 baud.
• Selectable parity – odd, even or none.
• Address range – 1 to 99.
For MODBUS communications to operate correctly, each DATUM L150/L160 must
be configured with the correct serial transmission parameters and assigned a
unique address.
3.1 Accessing the Configuration Mode
The procedure for accessing the Configuration Mode is detailed in Section 4.2 of
the relevant
User Guide. When all parameters have been programmed, return the
instrument to the Operator Mode.
3.2 Setting the Serial Transmission Parameters – Fig. 3.1
Fig. 3.1 shows the display readouts and options available when defining the serial
transmission rate and bit parity for DATUM L150/L160 instruments. Further detail
on the procedures required to set each parameter are shown in Section 4.3 of the
relevant User Guide.
3.3 Setting the MODBUS Address
To allow the master to differentiate between more than one slave in a system, each
slave on a MODBUS link must be assigned a unique address in the range 1 to 99
– see Section 4.4 of the relevant
User Guide (MODBUS Address Frame, Addr).
Display Parity
0 None
1Odd
2 Even
S 0000t 0000
S – Serial Communication Configuration T – Serial Communications Parity
Display Baud Rate, 2/4-wire
0Off
1 2400, 2-wire
2 2400, 4-wire
3 9600, 2-wire
4 9600, 4-wire