AT Commands: AT+CMGR works fine but AT+CMGL results in no response from GSM modem

2
votes

I'm using PUTTY to communicate (AT commands) with a Huawei E1750 GSM Modem. Sometimes, the AT+CMGL command does not work, and i wonder if anyone has any ideas what I could have made for mistake. If I remove the GSM modem from the usb and insert it again, the command works (meaning AT+CMGL works sometimes). But after some undefined time it results in no response like the image shows. I have tried resetting the modem using at commands, but have not succeeded. Could this be a bug with the E1750 GSM Modem, or what have I made for mistake?

enter image description here

2
serial-portsmsputtyat-command
By resetting the modem using at commands you mean ATZ or AT&F I assume? – hlovdal
Yes, correct. Have no effect. – Zeezer

2 Answers

1
votes

I can see no mistakes in your AT command handling here, so to me this seems to be a bug in the modem.

In particular the missing Final Result Code from the AT+CMGL="ALL" is not like it should be. And also for all the other commands there is echo so the command is repeated (e.g. "AT\rAT\r\nOK\r\n"), but not so for the AT+CMGR=5 command that follows the "black hole" AT+CMGL="ALL" command.

Some questions and suggestions for further testing/debugging:

  • Is the AT+CMGR=5 text you got here the actual AT command you enter interactively and then there was no additional echo from the modem, or did you enter the command "blindly" with the text shown being the echo from the modem?

  • Does the behaviour described in the point above apply to any command entered after AT+CMGL="ALL", or only other message related AT commands? Is there any timing component involved here (e.g. how long after AT+CMGL="ALL" was entered before the next command comes)?

  • Does this apply in PDU mode as well?

  • Does this apply to all the different message storages (check AT+CPMS)?

  • For USB there is almost always two serial interfaces available. Have you tested having both open at the same time? Does it make any difference to run an AT command on the other serial interface between AT+CMGL="ALL" and the next command? Will running AT+CMGL="ALL" on one interface have any effect at all on the other one?

  • Have you tried with different operating systems? Different terminal programs? (This really ought not to make any difference, but who knows)

-1
votes

I just stumbled over the same issue, and getting a new SIM card solved it. Communication with the modem now works fine. Hope this helps !