Difference between ATD and ATDT


I use

ATDT number

command to make a data call. But i realised that there is no explanation about ATDT command in documantation. There is only ATD command described in documantation. So, should i better change my ATDT implementation with ATD ? Does it make any difference?


ATD is the original Hayes “Dial” command

ATDT was added to specify “Tone” (as opposed to “Pulse” or “Loop-Disconnect”) dialling for PSTN lines.

Obviously, this has no meaning to a GSM modem. Some GSM modems accept it as a synonym for ATD.

Since ATD is the most general, I think that would be the better choice (most PSTN modems can be configured to use Tone dialling for ATD anyhow).