Campbell SDM-SIO1A User manual

INSTRUCTION MANUAL
SDM-SIO1A
Serial Input/Output Module
Preliminary: 5/16
Copyright © 2016
Campbell Scientific, Inc.

Limited Warranty
“Products manufactured by CSI are warranted by CSI to be free from defects in
materials and workmanship under normal use and service for twelve months
from the date of shipment unless otherwise specified in the corresponding
product manual. (Product manuals are available for review online at
www.campbellsci.com.) Products not manufactured by CSI, but that are resold
by CSI, are warranted only to the limits extended by the original manufacturer.
Batteries, fine-wire thermocouples, desiccant, and other consumables have no
warranty. CSI’s obligation under this warranty is limited to repairing or
replacing (at CSI’s option) defective Products, which shall be the sole and
exclusive remedy under this warranty. The Customer assumes all costs of
removing, reinstalling, and shipping defective Products to CSI. CSI will return
such Products by surface carrier prepaid within the continental United States of
America. To all other locations, CSI will return such Products best way CIP
(port of entry) per Incoterms ® 2010. This warranty shall not apply to any
Products which have been subjected to modification, misuse, neglect, improper
service, accidents of nature, or shipping damage. This warranty is in lieu of all
other warranties, expressed or implied. The warranty for installation services
performed by CSI such as programming to customer specifications, electrical
connections to Products manufactured by CSI, and Product specific training, is
part of CSI's product warranty. CSI EXPRESSLY DISCLAIMS AND
EXCLUDES ANY IMPLIED WARRANTIES OF MERCHANTABILITY
OR FITNESS FOR A PARTICULAR PURPOSE. CSI hereby disclaims,
to the fullest extent allowed by applicable law, any and all warranties and
conditions with respect to the Products, whether express, implied or
statutory, other than those expressly provided herein.”

Assistance
Products may not be returned without prior authorization. The following
contact information is for US and international customers residing in countries
served by Campbell Scientific, Inc. directly. Affiliate companies handle repairs
for customers within their territories. Please visit www.campbellsci.com to
determine which Campbell Scientific company serves your country.
To obtain a Returned Materials Authorization (RMA), contact CAMPBELL
SCIENTIFIC, INC., phone [phone]. After an application engineer
determines the nature of the problem, an RMA number will be issued. Please
write this number clearly on the outside of the shipping container. Campbell
Scientific’s shipping address is:
CAMPBELL SCIENTIFIC, INC.
RMA#_____
815 West 1800 North
Logan, Utah 84321-1784
For all returns, the customer must fill out a “Statement of Product Cleanliness
and Decontamination” form and comply with the requirements specified in it.
The form is available from our website at www.campbellsci.com/repair. A
completed form must be either emailed to [e-mail] or faxed to
[phone]. Campbell Scientific is unable to process any returns until we
receive this form. If the form is not received within three days of product
receipt or is incomplete, the product will be returned to the customer at the
customer’s expense. Campbell Scientific reserves the right to refuse service on
products that were exposed to contaminants that may cause health or safety
concerns for our employees.

Safety
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.com or by
telephoning [phone] (USA). 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, 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.

Contents
1. Introduction................................................................. 1
2. Specifications ............................................................. 2
2.1 Supported data rates and protocols ...........................................................2
2.2 Electrical parameters.................................................................................3
2.2.1 SDM-SIO1A current consumption.................................................3
2.2.2 SDM-SIO1A 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-SIO1A to other equipment................9
3.3.1 RS-485/RS422 Full duplex, one to one connection example.........9
3.3.2 RS-485 multi unit / in line example ...............................................9
3.3.3 RS-485 half duplex wiring example.............................................10
3.3.4 RS-485 internal circuit diagram...................................................10
3.3.5 RS-232 wiring example with handshaking...................................11
3.3.6 RS-232 basic 3-wire example ......................................................11
3.3.7 Connecting a 9 way socket to the SDM-SIO1A...........................12
3.4 Power conservation................................................................................12
4. Programming the datalogger................................... 13
4.1 Special information about the Serial I/O CRBasic commands when
used with the SDM-SIO1A .....................................................................13
4.1.1 SerialOpen ....................................................................................13
4.1.2 SerialClose....................................................................................15
4.1.3 SerialIn..........................................................................................16
4.1.4 SerialOut .......................................................................................16
4.1.5 SerialInBlock ................................................................................16
4.1.6 SerialOutBlock..............................................................................16
4.1.7 SerialInChk ...................................................................................17
4.1.8 SerialInRecord ..............................................................................17
4.1.9SerialFlush.....................................................................................17
4.1.10 Serial Input Errors.......................................................................17
4.2 Configuring handshaking and receive only modes..................................17
4.2.1 Using RTS/CTS and automatic handshaking ................................17
4.2.2 RS-485 half-duplex mode .............................................................18
4.2.3 Using the RS-232 link in receive only mode.................................18
4.3 Example datalogger programs.................................................................18
5. Firmware upgrades and flash signature errors...... 21
5.1 Upgrading the firmware ..........................................................................21
5.2 Firmware signature errors .......................................................................21
5.3 Checking the firmware version and signature .........................................21

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-SIO1A connections (left to right as viewed from the front)...........6
3-3. SDM-SIO1A Functional description of the connections .........................7
3-4. Pin cross connection table for SDM-SIO1 to SDM-SIO1A ....................8
4-1. Communications port parameters RS-232 .............................................14
4-2. Communications port parameters RS-485 full duplex...........................14
4-3. Communications port parameters RS-485 half duplex ..........................15
4-4. Communications port parameters RS-232 receive only mode ...............15

1
SDM-SIO1A Serial Input/Output Module
The SDM-SIO1A 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. The SDM-SIO1A is a functional replacement for the SDM-SIO1 interface, being
slightly smaller and having different labelling for some terminals (see Section 3.1.1).
SDM-SIO1A Serial Input/Output Module
1 Introduction
The SDM-SIO1A 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-SIO1A will accept serial data and store it in its buffer, which is 6143
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-SIO1As 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-SIO1A 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

SDM-SIO1A Serial Input/Output Module
2
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.
The SDM-SIO1A 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-SIO1A, 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-SIO1A 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-SIO1A 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-SIO1A 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-SIO1A 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-SIO1A.
Miscellaneous information
•The SDM-SIO1A does not support auto baud rate detection or use of the
serial port for general PakBus communications.
Buffer sizes
•Transmit buffer size: 767 Bytes (Buffer from the logger to the sensor)
•Receive buffer size: 6143 Bytes (Buffer from the sensor to the logger)

User Guide
3
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
discarded until space is made when the logger requests data from the
SDM-SIO1A.
2.2 Electrical parameters
2.2.1 SDM-SIO1A current consumption
Nominal
Max
Notes
General currents
Standby current
110 uA
150 uA
Current after SerialClose has been called.
RS-232 and RS-485 current consumption (1)
Idle current
4.8 mA
6 mA
After SerialOpen has been called
Idle current (receive only)
3.2 mA
4.5 mA
After SerialOpen in receive only mode
Active current (RS-232)
9.6 mA
12 mA
Active RS-232 command
Active current (RS-485)
11.7 mA
13 mA
Active RS-485 command (no termination
resistors)
Line load currents
RS-232 line load
2 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.9 of this manual shows the circuit in
detail.

SDM-SIO1A Serial Input/Output Module
4
2.2.2 SDM-SIO1A voltage specifications
Connection
Minimum
voltage
(1)
Nominal
voltage
(1)
Maximum
voltage
(1)
Power supply, +12V
connection
(2)
7V
12V
30V
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-485 input
(Differential)
200mV(4)
-
6V
RS-485 output
(Differential)
1.5V (at 50
Ohms)
-
-
SDM lines (high level)
4.5V
5V
5.5V
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-SIO1A 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-SIO1A 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
-40ºC
+70ºC
Humidity
Minimum
Maximum
Notes
Standard range
0%
95%
(non-condensing)

User Guide
5
2.4 Physical parameters
Main body
Height: 64 mm (2.51”)
Width: 62.5 mm (2.46”)
Depth: 22 mm (0.86”)
Main body including base mounting flange
Height: 64 mm (2.2”)
Width: 85 mm (3.35”)
Depth: 23 mm (0.86”)
Weight: 70g
Mounting centres are 76.2 mm (3”)
2.5 Datalogger compatibility
The SDM-SIO1A is compatible with our CR6, 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-SIO1A is normally mounted on the backplane of a Campbell Scientific
enclosure using the screws and plastic inserts provided. The SDM-SIO1A 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-SIO1As on a single SDM bus. Each SDM-SIO1A
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-SIO1A or not, then the user
will have to ensure their addresses are not the same.

SDM-SIO1A Serial Input/Output Module
6
Table 3-1. SDM address settings
Rotary switch
position
SDM address
SerialOpen
command
COMPort
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-SIO1A having an address of ‘0’ not ‘F’.
3.1 Connections
Connection to the SDM-SIO1A is achieved via the 11 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 the orange tab down with the
tip of a small flat blade screwdriver. Release the clamp and make 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.
When making connections to the datalogger always ensure power to the datalogger
is switched off and connect the ground (G) connection first.
Always use screened cable when connecting to the communications
connections.
.
NOTE

User Guide
7
Below is a table showing all the connections on the SDM-SIO1A.
Table 3-2. SDM-SIO1A connections
(left to right as viewed from the front)
Power SDM Communications connections
12V
G
C1
C2
C3
RG G
RTS/TD+
Tx/TD
-
Rx/RD+
CTS/RD
-
1 2 3 4 5 6 7 8 9 10 11
Table 3-3. SDM-SIO1A Functional description of the connections
Pin Case text Connection to Description
1 12V
Logger
Power supply. +12V
2 G Power supply 0V – Same as other ‘G’ pin
3 C1 SDM data enable line
4 C2 SDM clock line
5 C3 SDM data line
6 RG
Equipment
RG – RS485 ground. Connected to ‘G’ via 100R 1Watt resistor.
7 G 0V – Same as other ‘G’ pin
8 RTS/TD+ RS232 RTS. RS485 half-duplex non-inverting. RS485 Full
duplex outgoing.
9 Tx/TD- RS232 Transmit. RS485 half-duplex inverting. RS485 Full
duplex outgoing.
10 Rx/RD+ RS232 Receive. RS485 receiver non-inverting. RS485 full
duplex incoming.
11 CTS/RD- RS232 CTS. RS485 receiver inverting. RS485 full duplex
incoming.
CAUTION
The power ground connection to the datalogger should
be made with large gauge wire, e.g. 16 AWG or 1.5 mm2to
provide a low impedance path to ground to allow full
protection from static and electrical transients.
(1) The ‘G’ (pin 7) can be used for the RS-232 zero volt reference or any other
ground connection needed, e.g. shields.
(2) Connection `RG’ (pin 6) has 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.

SDM-SIO1A Serial Input/Output Module
8
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.
3.1.1 Matching SDM-SIO1A connections to the older SDM-SIO1
The SDM-SIO1A has less terminals and different labelling compared to the SDM-
SIO1. It does however perform in exactly the same way and can be used as a drop
in substitute with only minor changes to the wiring. It has less terminals because
the Z, Y, B and A terminals are not present. For the SDM-SIO1 these terminals
were connected internally to the TX, RTS, CTS and Rx terminals respectively and
were therefore duplicates. RS422 and RS485 devices can be connected to the
equivalent multifunction terminals on the SDM-SIO1A.
The labelling for the RS422/RS485 functions has also been changed to avoid the
confusion caused by different labelling conventions used for the A and B terminals
by different manufacturers. To avoid this the SDM-SIO1A uses the alternative
TD-, TD+, RD-, RD+ scheme of labelling, with the TD- and TD+ pair being those
used for RS485 half-duplex connections. Please refer to Table 3-4 for a cross
comparison between the connections for the SDM-SIO1 and the SDM-SIO1A.
Table 3-4 Pin cross connection table for SDM-SIO1 to SDM-SIO1A
SDM-SIO1 SDM-SIO1A
Case Text Pin Pin Case Text
C1 1 3 C1
C2 2 4 C2
C3 3 5 C3
G 4 2 G
+12V 5 1 +12V
G 6 7 G
RX-A 7 10 Rx/RD+
CTS-B 8 11 CTS/RD-
RTS-Y 9 8 RTS/TD+
TX-Z 10 9 Tx/TD-
0V 11 6 RG
Z 12 9 Tx/TD-
Y 13 8 RTS/TD+
B 14 11 CTS/RD-
A 15 10 Rx/RD+

User Guide
9
3.2 Safety considerations
The SDM-SIO1A 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 2.2.2 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.
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 RG line in the SDM-SIO1A, 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-SIO1A to other equipment
3.3.1 RS-485/RS-422 Full duplex, one to one connection example
To logger
RS485 0V
RS485 RD+
RS485 RD-
RS485 TD+
RS485 TD-
First RS485
equipment
with
termination
resistors
RS485 0V can be connected
straight to 0V but, this is not
recommended for long wire
lengths.
* Note connection order
+12V
G
C1
C2
C3
RG
G
RTS/TD+
TX/TD-
RX/RD+
CTS/RD-
R
R
Optional 100R resistors

SDM-SIO1A Serial Input/Output Module
10
3.3.2 RS-485 multi unit / in line example
RS485 0V
RS485 RD+
RS485 RD-
RS485 TD+
RS485 TD-
To logger
Second RS485
equipment
with
termination
resistors
* No RD-onnection order
RS485 0V
RS485 RD+
RS485 RD-
RS485 TD+
RS485 TD-
First RS485
equipment
with
termination
resistors
RS485 0V can be connected
straight to 0V but, this is not
recommended for long wire
lengths.
* Note connection order
+12V
G
C1
C2
C3
RG
G
RTS/TD+
TX/TD-
RX/RD+
CTS/RD-
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-SIO1A).
3.3.3 RS-485 half duplex wiring example
To logger
RS485 0V
RS485 RD+
RS485 RD-
RS485 TD+
RS485 TD-
First RS485
equipment
with
termination
resistors
RS485 0V can be connected
straight to G but, this is not
recommended for long wire
lengths.
* Note connection order
+12V
G
C1
C2
C3
RG
G
RTS/TD+
TX/TD-
RX/RD+
CTS/RD-
NOTE

User Guide
11
3.3.4 RS-485 internal circuit diagram
22R
22R
22R
22R
R
R
External
Internal
100R or higher *
100R or higher *
* Note the external termination resistors are optional. Some applications can use much higher
value resistors and some may not need resistors at all depending on the distance and wire quality
involved.
If the termination resistor is primarily needed for impedance matching then a value matching the
line resistance will have to be used.
100R
RG
0V
CTS/RD-
RX/RD+
TX/TD-
RTS/TD+
RX
TX
`RG’ is for connecting the screen/ground of the data lines when in RS485 mode,
there’s a 1W 100Ω resistor in series designed to limit any currents that may be
induced due to a difference in ground potentials between the sensor and the SDM-
SIO1.

SDM-SIO1A Serial Input/Output Module
12
3.3.5 RS-232 wiring example with handshaking
0V
RS232 RX
RS232 CTS
RS232 RTS
RS232 TX
To logger
RS232 DCE
equipment
* Note CTS and RTS are optional if hardware
handshaking is not required. Not connecting the
handshaking lines will reduce the overall current
consumption of the SDM-SIO1.
DTE DCE
+12V
G
C1
C2
C3
RG
G
RTS/TD+
TX/TD-
RX/RD+
CTS/RD-
3.3.6 RS-232 basic 3-wire example
0V
RS232 RX
RS232 RTS
RS232_CTS
RS232 TX
To logger
RS232 DCE
equipment
DTE DCE
+12V
G
C1
C2
C3
RG
G
RTS/TD+
TX/TD-
RX/RD+
CTS/RD-