Application Note: Using a GSM modem with a MicroLogix PLC
The objectives are:
1) To achieve serial communications between the 8-pin female mini-din connector of the PLC and
the 15-pin female connector on the Intercel SAM10E GSM modem.
2) To achieve bi-directional SMS message handling between the PLC and the Modem
3) To effectively analyse incoming SMS messages for origin and content, in order to control PLC
outputs and
4) To generate appropriate return acknowledgement messages or PLC input generated messages if
required.
The modem and the PLC can both be considered as DCE devices from a serial communications
perspective. It is possible to adjust communications parameters at both ends of the system using
RSLogix 500 for the PLC, and Hyperterminal or similar for the Modem. Obviously there will be
multiple options for establishing effective communications; the following is one tested method.
It is assumed that the reader is familiar with RSLogix 500 and Hyperterminal.
Attached reference documents:
AT_Command_Interface_Guide.pdf
This document outlines all relevant AT commands for the Intercel GSM modem- you’ll need to read
the relevant command descriptions if you wish to gain an understanding of how the system works.
ASCII TESTING ONE.RSS
The first test program, use this to test serial communication between the PLC and Hyperterminal. At
four rungs of ladder code, this example is extremely simple.
SMS CODE DEMO.RSS
The second test program, use this to establish basic functional SMS messaging to and from the PLC.
This code handles transmission and receipt of SMS messages by the PLC, predominantly through
string manipulation. Fuller details of code function are contained within comments in the code.
Required Hardware:
1) Intercel SAM10E GSM modem kit, including DB15 – DB9 cable
2) A valid SIM card for the Modem
3) DB9M-DB9M asynchronous modem eliminator, such as www.blackbox.com.au ME213
4) Micrologix Processor (tested with 1100, should be fine with 1200, 1400, 1500) with the ability
to activate inputs 0 and 1, and observe outputs 0 and 1.
a. If using Micrologix 1100 or 1400, a short Ethernet CAT-5e patch cable to make
programming a separate function from serial communications testing.
5) Micrologix Programming Cable 1761-CBL-PM02
6) A PC with hyperterminal
7) A mobile phone for testing purposes
