Hi,
Not sure if this is really the best place to post this question, but here goes....
I'm working with an arduino Mega and a SM5100B GSM module. I've been playing with some code for sending and receiving SMSs.
Occasionally I have to use the commands 'AT+CMGF=0' and 'AT+CMGF=1' to switch between 'text' mode and 'PDU'. I'm not sure of the reasoning behind this but it seems I need be in 'text' mode to read SMSs from the SIM card, and in 'PDU' mode if I want to send text messages longer than 140 characters.
Anyway, my question is, does the command 'AT+CMGF=?' just talk to the GSM module, or does it need to also communicate with the mobile phone network? The reason I ask is that on the bench (where I know the signal strength is good) I always get a response very quickly (a few milliseconds), but when moving this command sometimes takes a second or two to get a response, my guess is this happens where I have little or no signal.
Just to clarify, everything works ok, I'm not looking for a solution to a problem, I'm just curious what this command is talking to, the SMS modem, or the GSM network?
Cheers