If your controller is transferring data via modem, you can begin troubleshooting by entering Information Mode. You can then check the status of relevant System Bits and Integers to help diagnose the problem.
To begin diagnosing the problem, check the error code contained in SI 70. Refer to the error code table in How the M90 works with a modem.
The tables below show the more common causes of modem communication problems.
Problem |
SI 70 value |
Possible Cause & Recommended Action |
Modem fails to initialize |
2: Modem Did Not Reply |
PLC-to-modem cable: Make sure that the cable is securely connected. Check the modem connection and pin-out of the PLC-to-modem adapter cables. Note that if you use cables comprising this pin-out, you must set the RS232 parameter Flow Control to N (none). |
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Incompatible communication settings. Most modems automatically match the parameters of incoming data: baud rate, data bits, parity & stop bits. The M90's embedded modem settings are: 9600, 8 data bits, no parity, 1 stop bit. You may need to manually change your modem's communication settings to match these. |
|
0: No Error |
SB 72 OFF: In order to work with a modem, you must select 'Use modem' in the M90 Modem Configuration box . This causes SB 72 Initialize Modem to turn ON when the M90 powers up. Note that if the M90 has also been configured to use SMS messaging, that the M90 will not be able to connect to a modem because the SMS feature overrides the modem. Check too, that SB 72 is not disabled in your program. |
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6: Modem Report Error |
Check the modem initialization commands. Refer to Configuring the M90 to use a modem. |
Other problems:
Problem |
Possible cause |
Recommended action |
Modem is busy |
Modem is engaged |
Check that the modem is free. |
Connection established, but the PLC does not reply |
Modem adapter cable |
Check the PLC modem adapter cable pin-out, particularly that the DSR is connected to the RTS on the modem side. |
PLC does not dial |
Incorrect phone number |
Check the PLC's phone book. Refer to Configuring the controller to use a modem. |