For many years users of GX IEC Developer have wanted to remotely program a PLC via a serially connected GSM modem, however, the modem settings selection is “greyed out”. This document explains how to access these GSM modem settings.

Design Constraints

When attempting to program a remote PLC via a GSM modem, the problem has always been the variability of timing between sending a message and getting a reply. Serial communications always has “timeout” settings but the normal direct connection settings are typically too fast for GSM modem data transfer.

To enable the GSM modem options, you first have to select “via MAC/MTA transparent mode” in the “PLC side I/F” choices part of the “Transfer setup” settings.

This can be found from the Online menu then Transfer Setup, then Ports as shown below.

Once the “via MAC/MTA transparent mode” setting has been made and saved, the GSM modem settings can be accessed as shown below.

The main GSM timing setting above (default 1000ms) can now be adjusted to give reliable communications. The “Use additional synchronisation for direct memory access” setting is optional but probably worth configuring in addition to the basic setting.

NOTE: the settings above are not directly linked to the modem dial-up facilities available through the Transfer Setup menu.

Further Information – For further information, please refer to the help facilities in GX IEC Developer.

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