PLC to Modem Connections and Pin-outs

The next two figures show the basic elements you use to connect a controller to a modem.



Jazz (Add-on Port Module required)



M90/91 controllers

  • Comprise an integral COM port

  • Note that the M90/91 PLC programming cable is a 4-wire cable. The cable is included with the M90/91 all-in-one kits.

Jazz controllers

  • Do not comprise COM ports. To provide Jazz with a port, install an add-on port module. These may be part of a kit, or ordered separately. An example of a port module is the MJ20-PRG, included in the Jazz Programming Kit JZ-PRG.

  • Note that the Jazz PLC programming cable is a 6-wire cable. The cable is also included in the JZ-PRG kit.


Connecting a Controller to a Modem

You can:

General Information: Modem to Controller Interface (DCE to DTE)

The next figures show the interface between the Data Communications Equipment (DCE; the modem) and the Data Terminal Equipment (DTE; the controller or PC).  The arrows show the direction of data flow.

Note that:





Unitronics controllers do not support all the control lines.

Modems should be initialized via the Modem Services> Prepare Modem procedure. This procedure:

  • Turns the DSR signal ON

  • Turns the DCD signal ON (Jazz only)

  • Sets the appropriate PLC-modem communication parameters. These are:
    - M90/91: 19200 bps, 8 bit, no parity, 1 stop bit
    - Jazz: 9600 bps, 8 bit, no parity, 1 stop bit

Connecting DSR and RTS signals causes the modem to be always ready to transmit\receive data.

Using Modem Kits

Unitronics' kits contain all of the elements you need to connect a controller to a modem using the appropriate PLC programming cable, as shown in the first two figures at the beginning of this section.

Note that you must remove the PC adapter from the PLC programming cable and replace it with the modem adapter supplied in the kit.

In order to work with Unitronics controllers, you must initialize the modem via the procedure detailed in the Prepare PLC Modem topic.

The following list shows modem adapters supplied with the kits and their pin-outs. For updated information, consult your Unitronics distributor.

Standard Landline and Siemens GSM/GPRS modems

Sony Ericsson GM29 and Enfora GSM/GPRS modems

Wavecom GSM/GPRS modems


Wavecom modem kits do not contain the PC to modem cable, MJ10-22-CS32, that is required for the Wavecom Prepare Modem procedure. This cable is available by separate order.

Using a Unitronics Adapter

If you are using a modem from an independent source, you can order one of the modem adapters described in the preceding section from Unitronics, and use this adapter to connect your modem to the PLC via the PLC programming cable.

Constructing Adapters

You can construct a D-type modem adapter yourself, using the appropriate pin-outs shown in the preceding section.

You can also construct a cable with 2 male D-type connectors, and then use it to connect a modem's serial port directly to the PC adapter on the PLC programming cable as shown in the next figure.


The tables below give the pin-outs of the programming cables, and show you an example of the pin connection you can use to construct a cable with 2 male D-type connectors to connect a PLC to a standard landline modem.

M90/91 4-wire Programming Cable

Jazz 6-wire Programming Cable