Hi Chris,

Thank you for your post.

I have since solved the problem which I reported. I had already tried your suggestion, since there was two way communication between the modem and hyperterm / PIC because I were receiving acknowledgements from the modem to some commands and error messages from others.

The commands which gave me errors were those which generated a transmission i.e. AT+CMGS or the command which transmits a previously stored message at some loction <i>, AT+CMSS. The response from the AT+CMSS was +CMS ERROR: 321 which suggested I were trying to transmit an invalid memory index, which I knew to be false as I had successfully transmitted the message in this location using hyperterminal! Annoyingly, there was no error reported when using the AT+CMGS command, it just sat there and no SMS was received on my phone!

I bolied the problem down to something with my PIC hardware / software. Moreover it was something to do with the transmission commands, as every other command worked.

I noticed that when I tried to transmit an message the power LED on the board 'dipped' in brightness --- further investigation led me to spot that the modem needed 2A peak for transmission, however the power supply I were using only could deliver 1.1A. This seemed enough when ONLY the modem was being powered and the commands were coming from hyperterm, however when all my PIC circuit were sucking juice and trying to transmit then there was not enough power for everything!

I am sure you will agree this is a real suctle problem! I would have thought that there would have been some 'transmission error' messages which would be returned in situations like this - some feedback for the user!

What project are you working on? Are you using a GSM modem?

Regards

Tom