Campbell SDM-SIO1 User manual

SDM-SIO1
Serial Input/Output
Module
Issued: 5.1.15
Copyright © 2006-2015 Campbell Scientific Ltd.
CSL 627
USER GUIDE

Guarantee
This equipment is guaranteed against defects in materials and workmanship.
This guarantee applies for twelve months from date of delivery. We will repair
or replace products which prove to be defective during the guarantee period
provided they are returned to us prepaid. The guarantee will not apply to:

Equipment which has been modified or altered in any way without the
written permission of Campbell Scientific

Batteries

Any product which has been subjected to misuse, neglect, acts of God or
damage in transit.
Campbell Scientific will return guaranteed equipment by surface carrier
prepaid. Campbell Scientific will not reimburse the claimant for costs incurred
in removing and/or reinstalling equipment. This guarantee and the Company’s
obligation thereunder is in lieu of all other guarantees, expressed or implied,
including those of suitability and fitness for a particular purpose. Campbell
Scientific is not liable for consequential damage.
Please inform us before returning equipment and obtain a Repair Reference
Number whether the repair is under guarantee or not. Please state the faults as
clearly as possible, and if the product is out of the guarantee period it should
be accompanied by a purchase order. Quotations for repairs can be given on
request. It is the policy of Campbell Scientific to protect the health of its
employees and provide a safe working environment, in support of this policy a
“Declaration of Hazardous Material and Decontamination” form will be
issued for completion.
When returning equipment, the Repair Reference Number must be clearly
marked on the outside of the package. Complete the “Declaration of
Hazardous Material and Decontamination” form and ensure a completed copy
is returned with your goods. Please note your Repair may not be processed if
you do not include a copy of this form and Campbell Scientific Ltd reserves
the right to return goods at the customers’ expense.
Note that goods sent air freight are subject to Customs clearance fees which
Campbell Scientific will charge to customers. In many cases, these charges are
greater than the cost of the repair.
Campbell Scientific Ltd,
80 Hathern Road,
Shepshed, Loughborough, LE12 9GX, UK
Tel: [phone]
Fax: [phone]
Email: [e-mail]
www.campbellsci.co.uk

Precautions
DANGER —MANY HAZARDS ARE ASSOCIATED WITH INSTALLING, USING, MAINTAINING, AND WORKING ON
OR AROUND TRIPODS, TOWERS, AND ANY ATTACHMENTS TO TRIPODS AND TOWERS SUCH AS SENSORS,
CROSSARMS, ENCLOSURES, ANTENNAS, ETC. FAILURE TO PROPERLY AND COMPLETELY ASSEMBLE,
INSTALL, OPERATE, USE, AND MAINTAIN TRIPODS, TOWERS, AND ATTACHMENTS, AND FAILURE TO HEED
WARNINGS, INCREASES THE RISK OF DEATH, ACCIDENT, SERIOUS INJURY, PROPERTY DAMAGE, AND
PRODUCT FAILURE. TAKE ALL REASONABLE PRECAUTIONS TO AVOID THESE HAZARDS. CHECK WITH YOUR
ORGANIZATION'S SAFETY COORDINATOR (OR POLICY) FOR PROCEDURES AND REQUIRED PROTECTIVE
EQUIPMENT PRIOR TO PERFORMING ANY WORK.
Use tripods, towers, and attachments to tripods and towers only for purposes for which they are designed. Do not
exceed design limits. Be familiar and comply with all instructions provided in product manuals. Manuals are
available at www.campbellsci.eu or by telephoning [phone] (UK). You are responsible for conformance
with governing codes and regulations, including safety regulations, and the integrity and location of structures or land
to which towers, tripods, and any attachments are attached. Installation sites should be evaluated and approved by a
qualified engineer. If questions or concerns arise regarding installation, use, or maintenance of tripods, towers,
attachments, or electrical connections, consult with a licensed and qualified engineer or electrician.
General
•Prior to performing site or installation work, obtain required approvals and permits. Comply with all
governing structure-height regulations, such as those of the FAA in the USA.
•Use only qualified personnel for installation, use, and maintenance of tripods and towers, and any
attachments to tripods and towers. The use of licensed and qualified contractors is highly recommended.
•Read all applicable instructions carefully and understand procedures thoroughly before beginning work.
•Wear a hardhat and eye protection, and take other appropriate safety precautions while working on or
around tripods and towers.
•Do not climb tripods or towers at any time, and prohibit climbing by other persons. Take reasonable
precautions to secure tripod and tower sites from trespassers.
•Use only manufacturer recommended parts, materials, and tools.
Utility and Electrical
•You can be killed or sustain serious bodily injury if the tripod, tower, or attachments you are installing,
constructing, using, or maintaining, or a tool, stake, or anchor, come in contact with overhead or
underground utility lines.
•Maintain a distance of at least one-and-one-half times structure height, or 20 feet, or the distance
required by applicable law, whichever is greater, between overhead utility lines and the structure (tripod,
tower, attachments, or tools).
•Prior to performing site or installation work, inform all utility companies and have all underground utilities
marked.
•Comply with all electrical codes. Electrical equipment and related grounding devices should be installed
by a licensed and qualified electrician.
Elevated Work and Weather
•Exercise extreme caution when performing elevated work.
•Use appropriate equipment and safety practices.
•During installation and maintenance, keep tower and tripod sites clear of un-trained or non-essential
personnel. Take precautions to prevent elevated tools and objects from dropping.
•Do not perform any work in inclement weather, including wind, rain, snow, lightning, etc.
Maintenance
•Periodically (at least yearly) check for wear and damage, including corrosion, stress cracks, frayed cables,
loose cable clamps, cable tightness, etc. and take necessary corrective actions.
•Periodically (at least yearly) check electrical ground connections.
WHILE EVERY ATTEMPT IS MADE TO EMBODY THE HIGHEST DEGREE OF SAFETY IN ALL CAMPBELL
SCIENTIFIC PRODUCTS, THE CUSTOMER ASSUMES ALL RISK FROM ANY INJURY RESULTING FROM IMPROPER
INSTALLATION, USE, OR MAINTENANCE OF TRIPODS, TOWERS, OR ATTACHMENTS TO TRIPODS AND TOWERS
SUCH AS SENSORS, CROSSARMS, ENCLOSURES, ANTENNAS, ETC.

PLEASE READ FIRST
About this manual
Some useful conversion factors:
Area: 1 in2(square inch) = 645 mm2
Length: 1 in. (inch) = 25.4 mm
1 ft (foot) = 304.8 mm
1 yard = 0.914 m
1 mile = 1.609 km
Mass: 1 oz. (ounce) = 28.35 g
1 lb (pound weight) = 0.454 kg
Pressure: 1 psi (lb/in2) = 68.95 mb
Volume: 1 UK pint = 568.3 ml
1 UK gallon = 4.546 litres
1 US gallon = 3.785 litres
Recycling information
At the end of this product’s life it should not be put in commercial or domestic refuse
but sent for recycling. Any batteries contained within the product or used during the
products life should be removed from the product and also be sent to an appropriate
recycling facility.
Campbell Scientific Ltd can advise on the recycling of the equipment and in some cases
arrange collection and the correct disposal of it, although charges may apply for some
items or territories.
For further advice or support, please contact Campbell Scientific Ltd, or your local agent.
Campbell Scientific Ltd, 80 Hathern Road, Shepshed, Loughborough, LE12 9GX, UK Tel: +44 (0)
1509 601141 Fax: [phone]
Email: [email protected]
www.campbellsci.co.uk

Contents
1. Introduction.................................................................1
2. Specifications.............................................................2
2.1 Supported data rates and protocols ...........................................................2
2.2 Electrical parameters.................................................................................3
2.2.1 SDM-SIO1 current consumption ...................................................3
2.2.2 SDM-SIO1 voltage specifications..................................................4
2.2.3 EMC compliance ...........................................................................4
2.3 Temperature and humidity ranges............................................................4
2.4Physical parameters..................................................................................5
2.5Datalogger compatibility..........................................................................5
3. Installation ..................................................................5
3.1 Connections ..............................................................................................6
3.2 Safety considerations ................................................................................8
3.3 Examples for connecting the SDM-SIO1 to other equipment...................9
3.3.1 RS-485 one to one connection example.........................................9
3.3.2 RS-485 multi unit / in line example .............................................10
3.3.3 RS-485 half duplex wiring example.............................................11
3.3.4 RS-485 internal circuit diagram...................................................11
3.3.5 RS-232 wiring example with handshaking...................................12
3.3.6 RS-232 basic 3-wire example ......................................................12
3.3.7 Connecting a 9 way socket to the SDM-SIO1..............................13
3.4 Power conservation................................................................................13
4. Programming the datalogger...................................14
4.1 Special information about the Serial I/O CRBasic commands when
used with the SDM-SIO1........................................................................14
4.1.1 SerialOpen ....................................................................................14
4.1.2 SerialClose....................................................................................16
4.1.3 SerialIn..........................................................................................17
4.1.4 SerialOut .......................................................................................17
4.1.5 SerialInBlock ................................................................................17
4.1.6 SerialOutBlock..............................................................................17
4.1.7 SerialInChk ...................................................................................18
4.1.8 SerialInRecord ..............................................................................18
4.1.9 SerialFlush.....................................................................................18
4.1.10 Serial Input Errors.......................................................................18
4.2 Configuring handshaking and receive only modes..................................18
4.2.1 Using RTS/CTS and automatic handshaking ................................18
4.2.2 RS-485 half-duplex mode.............................................................19
4.2.3 Using the RS-232 link in receive only mode.................................19
4.3 Example datalogger programs.................................................................19
5. Firmware upgrades and flash signature errors......22
5.1 Upgrading the firmware..........................................................................22
5.2 Firmware signature errors .......................................................................22
5.3 Checking the firmware version and signature.........................................22

Appendix
A. Using the Handshaking lines for general input/output ...........................A-1
A.1 The input pin (CTS/pin 8)..............................................................A-1
A.2 The output pin (RTS/pin 9)............................................................A-2
Tables
3-1. SDM address settings ..............................................................................6
3-2. SDM-SIO1 connections (left to right as viewed from the front
of the unit)...............................................................................................7
3-3. SDM-SIO1 Functional description of the connections ............................7
4-1. Communications port parameters RS-232.............................................15
4-2. Communications port parameters RS-485 full duplex...........................15
4-3. Communications port parameters RS-485 half duplex ..........................16
4-4. Communications port parameters RS-232 receive only mode...............16

1
SDM-SIO1 Serial Input/Output Module
The SDM-SIO1 Module is designed to allow expansion of the number of serial ports
available on a datalogger for communicating with intelligent sensors or driving external
displays.
SDM-SIO1 Serial Input/Output Module
1 Introduction
The SDM-SIO1 Module connects to Campbell Scientific dataloggers using the
SDM port and communications protocol. It connects to the remote serial device
using industry standard hardware that can be set to RS-232, RS-485 or RS-422
signal levels. When operating in RS-232 mode it also supports hardware
handshaking. RS422 mode is functionally the same as RS485 mode except the
connection is limited to a point to point system. Connections and programming for
RS422 are otherwise identical to RS485.
The SDM-SIO1 will accept serial data and store it in its buffer which is 2047 bytes
in size allowing remote equipment to transmit large amounts of data without
needing to stop other processes in the datalogger.
Up to 15 SDM-SIO1s can be connected to a single logger using the SDM port,
allowing the user to connect 15 different items of equipment to their logger with
ease, in addition to any connections made to the dataloggers other serial ports.
To start using the SDM-SIO1 it is first necessary to work out how data will be
exchanged with a sensor. In the case of a sensor there are basically two options,
either the datalogger requests data and then picks up the response, or the sensor
transmits data “one-way” using its own timebase. The latter mode is more
common but can lead to problems with synchronising the sensor measurements
with the logger program and can also lead to the occasional missing data value as
there are two independent clocks. Once the method of communication and the
communications standard is defined then refer to Section 3 below on how to install
the module and connect it to the datalogger and the serial device.

SDM-SIO1 Serial Input/Output Module
2
The SDM-SIO1 Module is implemented in such a way that it looks like a built-in
serial port to the user when writing programs in CRBasic. This means all the user
needs to do is define the address of the SDM-SIO1, which is easily accomplished
by the use of a rotary switch on the side of the unit. The serial port can then be
used as if it were built into the datalogger. The only difference in operation
between the SDM-SIO1 and a built-in port is that there will be a small delay when
transferring data to and from the device via the SDM connection (see Section 4.1).
The SDM-SIO1 can also be used in `talk-through’ mode to allow a user to talk, via
a terminal module, to a sensor connected to the SDM-SIO1 for test and diagnostic
purposes. Please refer to the logger manual for further details.
Section 4 of this manual gives the differences in the use of this module compared
to the datalogger standard serial ports, plus there are some simple examples.
2 Specifications
2.1 Supported data rates and protocols
Data rates and protocols are set up using the SerialOpen command in CRBasic.
The SerialOpen command is discussed elsewhere in this document.
Supported data rates
300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, and 115200 bits/s
Supported modes of operation
RS-232 (Full duplex and receive only), RS-485 (Half and full duplex), RS-
422 (Half and full duplex). Hardware CTS/RTS flow control is supported in
RS-232 mode, the handshaking lines can also be used as general purpose I/O
lines.
Supported data format
8, 7 bit data size*; none, odd or even parity; one or two stops bits.
* In 7 bit mode with no parity the user must ensure that the characters
received by the SDM-SIO1 have a delay of at least one bit period or
greater between them. This does not affect any other configuration and
does not affect transmissions out of the SDM-SIO1.
Miscellaneous information
The SDM-SIO1 does not support auto baud rate detection nor the use of
the serial port for DNP, or general PakBus communications.
Use of the serial port for general Pakbus communications is not currently
supported.
Buffer sizes
Transmit buffer size: 767 Bytes (Buffer from the logger to the sensor)
Receive buffer size: 2047 Bytes (Buffer from the sensor to the logger)
Both transmit and receive buffers are fill and discard type, i.e. once the
buffers become full no new information is accepted and all further data is

User Guide
3
discarded until space is made when the logger requests data from the
SDM-SIO1.
2.2 Electrical parameters
2.2.1 SDM-SIO1 current consumption
Nominal
Max
Notes
General currents
Standby current
70 uA
100 uA
Current after SerialClose has been called.
RS-232 and RS-485 current consumption (1)
Idle current
5.5 mA
6 mA
After SerialOpen has been called
Idle current (receive only)
4.1 mA
4.5 mA
After SerialOpen in receive only mode
Active current (RS-232)
11. 5mA
12 mA
Active RS-232 command
Active current (RS-485)
12.5 mA
1 3mA
Active RS-485 command (no termination
resistors)
Line load currents
RS-232 line load
2 mA per
load
3 mA per
load
Average expected increase in drawn
current per RS-232 line connected in idle
or active modes (no extra current in
stand-by mode).
Both TX and RTS are considered to be
RS-232 loads.
RS-485 line load (2)
40 mA(3)
77 mA(4)
This extra current is only present when
actively transmitting
(1) All currents are measured with no loads connected
(2) The RS-485 transmit pair is disabled when not transmitting in order to save power higher
value resistors can be used to save power dependent upon the application. For many
applications, especially with shorter cable runs, no load/termination resistors will be needed.
(3) Single 100R load between transmit lines. Two 100R resistors (one on each end) is the
maximum recommended loading. Removing any termination resistance should dramatically
decrease current consumption during transfer of data
(4) The RS-485 interface is protected against short circuits via a 44R resistance making this the
maximum current possible even during short circuit. This resistance is part of the ESD
protection circuitry and will be present at all times; it shouldn’t affect normal circuit
operations. The ‘RS-485 internal circuit diagram’ on p.10 of this manual shows the circuit
in detail.

SDM-SIO1 Serial Input/Output Module
4
2.2.2 SDM-SIO1 voltage specifications
Connection
Minimum
voltage(1)
Nominal
voltage(1)
Maximum
voltage(1)
Power supply, +12V
connection(2)
7V
12V
20V
RS-232 input threshold
Low
0.8V
-
-
RS-232 input threshold
High
-
-
2.4V
RS-232 input absolute
maximum(2)
-
+/-15V
+/-18V
RS-232 input resistance
3 KΩ
5 KΩ
7 KΩ
RS-232 output voltage
swing(3)
+/-5V
+/-5.4V
-
RS-232 output absolute
maximum
-
-
+/-13.2V
RS-485 input
(Differential)
200mV(4)
-
6V
RS-485 output
(Differential)
2V (at 50
Ohms)
-
-
SDM lines (high level)
4.3V
5V
5.7V
SDM lines (low level)
0V
-
0.7V
(1) Values are volts D.C. (except resistances)
(2) It is NOT recommended that the user runs their SDM-SIO1 at maximum ratings for
extended periods of time
(3) Assuming a worst case 3 KΩ load
(4) It is not recommended that the user allows such low input voltages as there will be an
increased chance that external noise may cause errors in the incoming data
2.2.3 EMC compliance
The SDM-SIO1 has been tested and shown to comply with IEC 61326. The
device incorporates transient and surge protection that is designed to meet
IEC61000-4-5, level 4, providing the device is adequately grounded.
2.3 Temperature and humidity ranges
Temperature range
Minimum
Maximum
Notes
Standard range
-25ºC
+50ºC
Extended range
(optional)
-40ºC
+80ºC
(Contact Campbell
Scientific Ltd for further
extended temperature
requirements)
Humidity
Minimum
Maximum
Notes
Standard range
0%
95%
(non-condensing)

User Guide
5
2.4 Physical parameters
Main body
Height: 5.4H cm (2.2”H)
Width: 8.0W cm (3.1”W)
Depth: 2.5D cm (1.0”D)
Main body including base mounting flange
Height: 5.4H cm (2.2”H)
Width: 11.2W cm (4.5”W)
Depth: 2.5D cm (1.0”D)
Weight: 80g (approximately)
Mounting centres are 10.2cm (4”)
2.5 Datalogger compatibility
The SDM-SIO1 is compatible with our CR800, CR850, CR1000, CR3000,
CR5000, and CR9000X dataloggers. The CR5000 and CR9000X’s operating
system must be OS 6 or higher.
3 Installation
The SDM-SIO1 is normally mounted on the backplane of a Campbell Scientific
enclosure using the screws and plastic inserts provided. The SDM-SIO1 is
designed to be installed in a dry, non-condensing environment.
Before fixing it, select and set the SDM address as this requires access to the side
of the case. The SDM address is set with a screw driver. Below is a list of the
possible SDM addresses and their relationships to the COMport number in the
SerialOpen command.
There can be up to 15 SDM-SIO1s on a single SDM bus. Each SDM-SIO1 will
need to be set to a unique address before they are powered up; if any other
equipment is present on the bus, whether it’s an SDM-SIO1 or not, then the user
will have to ensure their addresses are not the same.

SDM-SIO1 Serial Input/Output Module
6
Table 3-1. SDM address settings
Rotary switch
position
SDM address
SerialOpen
command comm.
port number
0
0
32
1
1
33
2
2
34
3
3
35
4
4
36
5
5
37
6
6
38
7
7
39
8
8
40
9
9
41
A
10
42
B
11
43
C
12
44
D
13
45
E
14
46
F(1)
15(1)
47(1)
(1) Address ‘F’ is not available as it’s the broadcast address. Setting this address will result
in the SDM-SIO1 having an address of ‘0’ not ‘F’.
3.1 Connections
Connection to the SDM-SIO1 is achieved via the 15 terminals arranged along the
top of the unit. The terminals are spring loaded providing an easy and reliable
method of connection. Wires should be stripped 7-9 mm, twisted and inserted in
the round hole whilst opening the clamp by pushing a screwdriver in the adjacent
rectangular hole or by pushing a screwdriver into the hole on the side of the
connector. Remove the screwdriver to close the clamp making sure the clamp
grips the wire rather than the plastic insulation.
If there is a need to insert more than one wire in each terminal, if using multi-
strand wire twist the conductors together first. If using solid wires, either solder
or crimp multiple pairs together before insertion. For RS-485 connections note
that the RS-232 terminals double up as a secondary connection, so it is rare to have
multiple conductors in one terminal as both sets of connections can be used either
for forming an RS-485 daisy-chain or for adding termination resistors at each end
of a network.
When making connections to the datalogger always ensure power to the datalogger
is switched off and connect the ground (G) connection first.
Below is a table showing all the connections on the SDM-SIO1. There are a
number of pins that are common within the unit, these are also shown below.

User Guide
7
The A, B, X, Y notation used in the labelling of the SDM-SIO1 follows
the practice of the driver chip manufacturer (Maxim Inc.) used in this
product. Unfortunately, the convention of A/B and X/Y labelling differs
between different designers of RS485 products. If you cannot get the
connection to work with another device, or the data is completely
corrupted, please first check the polarity of the connections (see below)
for the SDM-SIO1 relative to the device it is being used with as they give
a more certain indicator of the correct connection than the A/B notation.
If the polarity is not indicated then reversing the A relative to B
connections (and the X and Y if used) can be done to check for the
correct connection with no risk of damage to either device.
Table 3-2. SDM-SIO1 connections (left to right as viewed from the front
of the unit)
SDM
Power
connections
RS-232 connections
RS-485/RS422
C1
C2
C3
G
+12V
G
RX-A
CTS-B
RTS-Y
TX-Z
0V
Z
Y
B
A
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
15
14
13
12
10
9
8
7
Note: Italic numbers indicate which pins are connected internally (for use with RS-485 termination
resistors etc.). For example the signals present on pin 7 will also be present on pin 15.
Table 3-3. SDM-SIO1 Functional description of the connections
N
Case text
Description
1
C1
SDM data line –connect to datalogger SDM C1
2
C2
SDM clock line –connect to datalogger SDM C2
3
C3
SDM enable line –connect to datalogger SDM C3
4
G
Connect to the datalogger power ground (G) (1)
5
+12V
Main power supply –connect to logger 12V
6
G
RS-232 0V reference/second G connection (2)
7
RX-A
RS-232 receive line
8
CTS-B
RS-232 CTS hardware handshaking line / output
9
RTS-Y
RS-232 RTS hardware handshaking / input
10
TX-Z
RS-232 transmit line
11
0V
RS-485 0V reference line (3)
NOTE

SDM-SIO1 Serial Input/Output Module
8
12
Z
‘-‘ RS-485 output line, line Z*
13
Y
‘+’ RS-485 output line, line Y*
14
B
‘-‘ RS-485 input line, line B*
15
A
‘+’ RS-485 input line, line A*
*See note above
(1) At least one of the two G terminals (‘G’) must be connected to the loggers ground
terminal or earth boss.
CAUTION
The ground connection to the datalogger should be made
with large gauge wire, e.g. 16/0.2 to provide a low
impedance path to ground to allow full protection from
static and electrical transients.
(2) The ‘G’ (pin 6) can be used for the RS-232 zero volt reference or any other
ground connection needed, e.g. shields.
(3) There is a 100R resistor in series with the dataloggers ground connection. This
connection should be used when connecting RS-485 equipment by long wire
lengths. It ensures both systems have a common ground reference point. See
Section 3.2 below before connecting.
As shown above in Table 3.3 connections 1 to 5 need to be made to the datalogger,
either connecting the SDM lines to the matching control ports or the dedicated
SDM port when fitted, e.g. the CR3000. The connection of the wires to the
remote serial device will vary with type of device and method of communication.
It is necessary to work out the best mode of operation of the serial device, taking
into consideration issues such as power consumption, cable lengths (RS-485 being
better than RS-232), synchronisation of data collection etc.
In Section 3.3 there are some examples of different connection schemes for the
serial devices. Further discussion of different modes of operation are given in
Section 4.
Do not connect both RS-232 and RS-485 interfaces to the SDM-SIO1 at the
same time as this may cause a bus contention and even possibly cause damage.
3.2 Safety considerations
The SDM-SIO1 is considered to be a component of a measurement system that is
installed in an enclosure and wired up in accordance with this manual. Due to
space considerations full details of the maximum ratings of the connections are not
given on the device. Instead the user should study this manual and in particular
Section 2.1.2 to determine the maximum voltages that are applicable to any
terminal before starting an installation.
The RS-485 0V ground reference connection may be needed to ensure all units are
referenced to a common ground voltage. This is more often needed with long
cable runs.
NOTE

User Guide
9
It is advisable to check the difference in ground potential with some caution before
connecting any wires, to ensure the potential differences are reasonably close and
excessive current will not flow between the two ground wires. There is a current
limiting resistor fitted in the 0V line in the SDM-SIO1, but this will not be
adequate in the event of a serious ground fault, e.g. the ground references being
240 V apart, due to faulty AC wiring. If a large potential difference is found
please seek the advice of a qualified electrician before continuing with the
installation.
3.3 Examples for connecting the SDM-SIO1 to other equipment
3.3.1 RS-485 one to one connection example
Notes:
Z, Y, B and A are connected to their corresponding differential wire pairs
when in RS-485/RS422 mode. Where A and Y are the ‘+’ lines and B
and Z are the ‘-‘ lines.
Connections 7-10 are connected internally to connections 12-15. This
allows for terminations resistors to be added when in RS-485 mode (if
needed) or, more than one connection to the I/O lines or TX and RX lines
in RS-232 mode.
If the use of termination resistors is required in RS-485 mode then they
should be connected between pins TX-Z and RTS-Y for the ZY line and
CTS-B and RX-A for the A B line (see diagrams elsewhere in document).
In half duplex RS-485/RS-422 mode the Z Y and A B pairs are connected
internally by the hardware without the need for any user interaction. The
user should connect their wires to ZX and YS, as ‘A’ and ‘B’ are
disabled.
C1
C2
C3
G
+12V
G
RX
-
A
CTS
-
B
RTS
-
Y
TX
-
Z
0V
Z
Y
B
A
RS-485 0V
RS-485_Z
RS-485_Y
RS-485_B
RS-485_A
R
R
To logger
RS-485
485
equipment
with
termination
n
resistors
100R or higher
1
2
3
4
5
6
7
8
9
10
-
Z
11
12
13
14
15

SDM-SIO1 Serial Input/Output Module
10
3.3.2 RS-485 multi unit / in line example
As with all RS-485 configurations the use of termination resistors is
optional. They tend not to be required with shorter cable runs and
with modern slew-rate limited driver technology (as used in the
SDM-SIO1).
NOTE
RS-485 0V
RS-485_Z
RS-485_Y
RS-485_B
RS-485_A
To logger
Second RS-485
equipment
* Not
connection orde
RS-485 0V
RS-485_
A
RS-485_
B
RS-485_
Y
RS-485_
Z
First RS-485
equipment
RS-485 0V
for ground
referencing
.
C1
C2
C3
G
+12V
V
G
RX
-
A
CTS
S
-
B
RTS
S
-
Y
TX
-
Z
0V
Z
Y
B
A
1
2
3
4
5
6
7
8
9
10
-
Z
11
12
13
14
15