4.Troubleshooting-guide
There is never a simple "no connection". There are many causes for this, which can be excluded step-by-step. If you never had a successful data-connection, you should test first with an analog modem at the other side. Also, if possible, avoid problems with local company-exchanges, using a direct phone-line. This applies specially if you call to a digital "modem" (ISDN-TA). You can test these configurations later. It is also helpful, to test different numbers on both sides. (ISDN/analog, direct/local exchange, mobile phone on called side. Different providers for GSM-Module.
It is very recommended to make all tests in both directions, because in many cases of failure, the other direction is working. This helps to find the error.
SIM-card recognized?
SIM-card can be tested by AT+CPIN? Answer: +CPIN: READY. (Answer :+CPIN: SIM
PIN : you should enter PIN first).
Verify the signal-quality
with AT+CSQ?. (repeat command a couple of times every 10secs.) It should never drop below 10, critical connections could work down to about 7. Find best antenna- location with mobile phone.
Network-attached?
To control that the module is connected to the network, you see the response of AT+CREG with the HEX-info about the cell. (First, enable CREG with AT+CREG=2)
DTE-baud-rates
Control if on both sides the data-rate of the DTE-DCE connection (of the computer- terminal) is set higher than 9600 (best is 115200 as default for all applications). The GSM-module can stay at autobaud (AT+IPR=0). For GPRS, set data-rate to 115200 baud.
If your application will work with lower DTE-rates, you can test these settings of AT+CBST later, because 9600 is the standard of many modems. (19200/2400/1200 not working always). Set baud-rate on GSM-Module: use AT+IPR command.
Regarding hyper-terminal: We made bad experiences with it, sometimes it hangs up and there is no comfort. We use Procomm 4.8 from Symantec, there you can also write very comfortable scripts with window-support. Also as a dumb terminal, it is much more reliable. They have also very good support in one day.
The following steps apply to analog-modems and ISDN-TA's (digital phone- connection).
Exceptions are marked.
