I am using SIM900 GSM module connect to my AVR Microcontroller. I tested it with FT232 to see transmitting data. First Micro sends AT it will response OK
AT OK
AT+CMGF=1 OK
AT+CMGS="+9893XXXXXX" returns ERROR and doesn't show ">"
Could anybody advise me what to do?
Command AT+CSCS? will answer You what type of sms-encoding is used. Properly answer is "GSM", and if not, You should set it by command AT+CSCS="GSM".
And remember about "Ctrl+Z" (not "Enter") as a finish of sms text, please.
You aren't passing all the parameters to the command.
The command format is:
AT+CMGS=<number><CR><message><CTRL-Z>
Where:
<CR> = ASCII character 13
<CTRL-Z> = ASCII character 26
You have passed only the number and without the <CR> you won't see the > note for the message.
Example:
AT+CMGS="+9893XXXXXX"
> This is the message.→
The response is:
+CMGS:<mr>
OK
Where <mr> is the message reference.
If AT+CSCS? command returns UCS2, then many arguments need to be encoded as hex string of UTF-16 encoding, so the phone number would become "002B0039003800390033...", and the SMS text would need to be encoded in the same way. If you don't need UCS2 encoding, then the easiest thing to do is to switch to GSM encoding (or another encoding from the available set as shown by AT+CSCS=? command)
Sometimes the issue is the text mode you are in. Enter AT+CMGF? and you should receive +CMGF: 1. If instead you receive +CMGF: 0, enter AT+CMGF=1. This changes the message format from PDU mode to Text mode. I'm not sure what either of those mean exactly, but this fixed my issue.
来源：https://stackoverflow.com/questions/21522794/atcmgs-returns-error