Most (or just about all) modems claim to be Hayes Compatible, meaning that it will understand most of the AT command language originating from the Hayes Company back in the '70's. Normally you won't need to know AT Commands to operate your modem, but sometimes the right instruction can get a stuck modem up and running again. Please bear in mind that not all commands will work with all modems, and that many modem manufacturers add to the basic Hayes language with their own proprietary (and useful) modem-specific AT Commands. To learn what these are, you may need to look at the modem's manual or the manufacturer's web site.

To use AT Commands, open Windows' HyperTerminal applet by selecting Start> Programs> Accessories and then double-clicking the Hypertrm.exe icon (In OSR2 and Windows 98, look in the Communications folder under Accessories).

 

Command	Function
AT DT xxx-xxxx	Dials the number xxx-xxxx
AT H	Disconnects current call
AT A	Answers incoming call
AT E1	Turns on echoing(use if your Communications Program doesn't display commands as you type)
AT Z	Resets the modem(essential for Internal Modems since you can't flip a power switch).
AT17	Displays modem's manufacturer,model & version number.
AT LO	Set lowest speaker volume.
AT & F(or AT & F1)	Restores modem to it's default factory settings.
A/ (without the AT prefix)	Repeats last command issued.
+++ (without the AT prefix)	Switches into Command Mode while you're connected.
AT OO	Returns you from Command Mode.