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Cellular Phone Forum / General / GSM / April 2005AT command problem
I am polling my GSM modem for new messages every 10 seconds... and it works fine for some 5 minutes or so and returns OK. after that it starts returning funny charracters. Character that looks like a small rectangle( some what like this []). I have tried this on wavecom and round solutions modems and its the same on both. any clues ? Cheeros Rishi > I am polling my GSM modem for new messages every 10 seconds... > and it works fine for some 5 minutes or so and returns OK. [quoted text clipped - 6 lines] > > any clues ? This looks like a speed (baud rate) or character framing (number of data or stop bits, or parity) problem. Is the modem set to auto-baud? What do "AT+IPR?", "AT+ICF", and "AT+WRST?" return? John Will try once i reach my place...but is it possible for the modem to function correctly for a while and then all of a sudden start returning junk if it is in autoo-baud ? Cheeros Rishi > Will try once i reach my place...but is it possible for the > modem to function correctly for a while and then all of a > sudden start returning junk if it is in autoo-baud ? It shouldn't be possible, but that doesn't mean it isn't happening :( Another possibility is that you're running at a fixed rate and character framing, and have got Wavecom reset (AT+WRST) set to 5 minutes (undoing your configuration). John Hi, I am using a round solutions modem now. My wavecom has some issues. wanted to ask u something. When i send AT command to the modem using my program...what is the best way of reading the return buffer. I mean how do i know when to stop reading. \r\n does not work for all commands... i look for the expected return, lets say OK when i send an AT command via my program and then i ignore what is after that and i flush before every send to the modem. Any good modem programming articles that u can point me to ? Cheers Rishi > Hi, > I am using a round solutions modem now. My wavecom has [quoted text clipped - 8 lines] > command via my program and then i ignore what is after that > and i flush before every send to the modem. The following works for me: I handle the reading of the buffer with a purpose-built subroutine. I pass it 2 (optional) parameters: the response-termination string I'm expecting (usually "\r\nOK\r\n"), and the number of seconds to wait for further input if I don't see that string. This means that I might get other responses as well (I also expect unsolicited responses like "+CREG:", "+CSQ:", "+CCED:" and "+CBM:"), and need to separate these outside of this subroutine. So I always check the buffer for every type of response that might be expected. If the response happens to be incomplete, I leave the incomplete part of the response string there so that the remainder of that response gets concatenated to it at the next call to the input subroutine. This input subroutine waits around for a half-second or so for further input in any case, and I find it works perfectly reliably. I hope that helps. > Any good modem programming articles that u can point me to ? http://www.programmersheaven.com/ is a good starting point. John setting the baud rate works.... hey do u know how i can turn off the RING and other such disturbing unsolicited responses :) cheers Rishi > setting the baud rate works.... > hey do u know how i can turn off the RING and other such > disturbing unsolicited responses :) I haven't tested it, but you could have a look at "AT+CMER" (perhaps "AT+CMER=0,0,0" might work, but you might lose output you need too). A better, more defensive programming approach is to deal with them. I keep the device output in a buffer string variable. I frequently search that string for all result code introducers that interest me, and process them in a logical, sensible order. Having dealt with one, I immediately destroy it (by overwriting a character, changing "+CBM:" to "+ BM:" for instance). At appropriate points, I shorten the string or clear it completely. For commands that don't produce a leading result code (like "AT+CGSN"), I temporarily turn command echo on, and take my cue from the echoed command instead. John Hi John, thanks for the help last time. The wavecom modem did not have GPRS stack enabled so i switched to a round solutions modem. I was able to send mail using AT command. Cheeros Rishi Some hints on the Round Solutions modem www.roundsolutions.com you will find on http://www.gsm-modem.de/gsm-modem-faq.html . Sending of emails is descripted on http://www.gsm-modem.de/smtp-gprs.html . Regards Meff Hi, I finally figured it out...it was the baud rate settings issue. Once is set it to 19200 using th AT+IPR it is quite ok now. One last problem remaining...when i enter the data mode...i cannot exit it... nothing happens when i send +++ also... :( its quite fun playing with the modem..but unfortunately round solutions documentation is not as good as wavecome... Cheers Rishi > One last problem remaining...when i enter the data mode...i > cannot exit it... > nothing happens when i send +++ also... :( Don't neglect the importance of the guard time. There must be a significant pause in the data stream both sides of the "+++" escape string (but not within it). I don't know what the default is, but 3 seconds should be more than sufficient. John I've experiences quite differing behaviour from various modems in response to the '+++' and 'ATH' commands. Some devices tolerate zero guard time, some definitely require it (though IMHO 3seconds is a lot...). One unit actually responded with an 'OK' to the '+++'. Be prepared :) I decided to turn to the 'drop DTR' method of hanging up - but if the OP only needs to enter command mode temporarily, that's of course not going to help him... Just my 2 cents.. Regards Per > > One last problem remaining...when i enter the data mode...i > > cannot exit it... [quoted text clipped - 6 lines] > > John > I've experiences quite differing behaviour from various modems > in response to the '+++' and 'ATH' commands. > Some devices tolerate zero guard time, some definitely require > it (though IMHO 3seconds is a lot...). One unit actually > responded with an 'OK' to the '+++'. Be prepared :) I think it should do that - it's going into command mode, after all. > I decided to turn to the 'drop DTR' method of hanging up - but > if the OP only needs to enter command mode temporarily, that's > of course not going to help him... A couple of further thoughts for Rishi: make sure that you haven't included a <carriage return> with the "+++". And because some systems will buffer the output (flushing with a <carriage return> for instance), you might need to read up on flushing the "+++" from the buffers in your compiler's documentation. John > I think it should do that - it's going into command mode, after > all. You could very well be right - the 'standards' leave a lot to the interpretation of manufactures and users, IMO. Anyway, two of three (Ericsson GM29 and Siemens TC35) do not respond with 'ok' to the '+++', one (OvisLink G??1500 PCMCIA - not sure about the exact p/n) does. /Per > You could very well be right - the 'standards' leave a lot to > the interpretation of manufactures and users, IMO. > Anyway, two of three (Ericsson GM29 and Siemens TC35) do not > respond with 'ok' to the '+++', one (OvisLink G??1500 PCMCIA - > not sure about the exact p/n) does. That's interesting. I'm not saying you're wrong, but the TC35 "AT Command Set" manual I've got clearly shows an "OK" response to "+++". I've never used a TC35 though. It goes on to specify a guard time of "1000 ms", and mentions that the three "+" characters must be sent "all within 1000 ms". As an aside, a modem with zero guard time could not be used to connect to an ISP and post this message - because it contains the "escape to command mode" sequence. John i solved my problem... I was making a mistake..i was hoping to disconnect from a smtp session using +++. The escape sequence works after i send a QUIT commands to the smtp and service channel is closed. I have to be able to send http packets over the gprs connection that i have established...Is it by anyway possible to direct my program to use the gprs connection instead of the normal lan that i use...? There is a class by the name of WebClient in .NET which handles http. I was hoping if i could redirect the communication via my gprs connection then i would not need to send http commands on the wire myself. Cheers Rishi I am using rasdial.exe and i call it from my program to dialup my gprs connection. then i can use .net's built in webclient class to access the internet. cheers Rishi > I finally figured it out...it was the baud rate settings > issue. Once is set it to 19200 using th AT+IPR it is quite ok > now. You might find that 9600 is a better choice for a Wavecom Fastrack modem, as that's what the DCE => DTE side will revert to after a reset using "AT+CFUN" or "AT+WRST". And for GPRS use, 57600 or 115200 are the realistic choices to get class 10 throughput. Personally, I like to use autobaud. You might need to save that setting to EPROM though, using "AT&W". John |
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