Modem Troubleshooting

Note ♦

The modem must reply with either OK or READY to each command entered. If the modem fails to answer, the command has not been processed.

+++

Escape Sequence. This causes the modem to close connections and go back to command mode

AT

This command means Attention; and is used to begin a session

AT&F

Restores factory default settings

ATZ

Resets the modem.  This command may take time to implement, so the response from the modem may be delayed

ATE0

No Echo

V1

Enable Verbose (long) response

Q0

Respond

X4

Detailed answers

&D0

Ignore DTR

&S0

DSR always ON.
Since the DSR can be permanently set to ON, connecting it to the RTS causes the terminal always be ready to transmit\receive data

&S1

DSR OFF in command and test modes

&C1

Give the user a signal for the DCD

ATS0=1

Auto-Answer after 1 ring

&W

Burn the configuration into the modem’s non-volatile memory

Message

Cause

COM Port not open, or modem does not exist

The PC was unable to access the PC port.

The port may:

 -Already be in use.

 -Be damaged.

Modem not connected

The PC receives no reply from the modem following the 'AT' command.

Check that:

 -The modem is connected to the same PC port you have defined in PC-modem Configuration.

 -The PC-modem cable is in proper order.

Modem not initialized

The modem was not successfully initialized, or

The modem answered, but did not approve all strings.

Check the topic: Using Hyperterminal for Modem Troubleshooting

The messages below describe the modem 's status if the PC dial attempt ( ATD+ number) fails.  Any one of these errors aborts the Dial process.

Modem Busy

Modem Error

No Dial Tone

No Carrier

Note ♦ This can occur if, within the modem initialization strings, the parameter S7 TimeOut, is to short to permit the PLC's modem to answer.

For example, if this parameter is set as S7=30, the PC modem will wait for 3 seconds to receive an answer from the PLC's modem. If, however, the PLC program's COM Init FB Answer Settings are set to 'Answer after 6 rings,' the PLC modem will not be able to answer before the 3 seconds have elapsed. In this case, the TimeOut parameter is exceeded, and the PC modem will return the No Carrier error.

Dial time-out exceeded

No reply was received from the modem within the defined time.

The messages below only relate to unsuccessful GSM modem initialization.

GSM SIM card blocked

GSM SIM card does not exist

Illegal GSM PIN code

GSM Network not found

  CDMA Network not found

SMS message too long

A message containing only English characters may contain up to 160 characters.

A message containing non-English characters may contain up to 70 characters.

Time-out exceeded

Message

Possible cause

Recommended action

Modem Busy

Modem is engaged,
or is being initialized

Check that the line is free.
Use the SBs: Modem Initialization Status listed above to check the COM port status; communications cannot flow through the port during initialization. For more information check the topic COM Port Init.

Handshake between modems complete ('CONNECT'),

PLC does not reply

Modem adapter cable

Check the  PLC-to-modem connection and pin-out, particularly that the DSR is connected to the RTS on the modem side.

Problem

SI Value (80, 82, 84)

Possible Cause & Recommended Action

Modem fails to initialize (SB 81, 83, 85 ON)

3

• 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 parameter Flow Control to N (none) in the COM Port Init FB.

• Incompatible communication settings.

Most modems automatically match the parameters of incoming data: baud rate, data bits, parity & stop bits. You may need to manually change your modem's communication settings.

0

You may have selected the wrong type of modem in the COM Port Init FB.

A complete list of error messages for SI 80, 92, 84, as well as other System Operands containing modem error is given in the topic COM Port/Modem Status, System Operands, & Error Messages.

Problem

SI Value (81, 83, 85)

Possible Cause & Recommended Action

Wrong PIN number

3

Check the PIN number in the COM Port Init FB; leave it empty if your SIM card has no PIN number.

Failed Registration

4

GSM modem did not register successfully, for example if no network was found, or if the modem antenna is not functioning.

PUK number needed

5

The SIM card is locked due to too many attempts to enter an incorrect PIN number.

Problem

Possible Cause & Recommended Action

Cell phone does not receive message

Check the cell phone's SIM card; it may be full. You can clear the SIM card using the Clear option in the COM Port Init FB.

PLC modem does not respond to cell phone call

GSM modems generally recognize whether the incoming call is voice or data. If the modem has been set to answer (via the ATS0=x command, where x is set to a value greater than 0), the modem will not answer an incoming cell phone call, since it will be recognized as a voice message.

Note ♦

The appropriate Modem: Initialized SBs [80 (COM 1), SB 82 (COM 2), SB 84 (COM 3)] must turn ON before activating an SMS Config FB using that COM port; ideally the SBs should be used as an activating condition.