For many years Hayes modems have been the standard in modems. As the field of modem manufactures has grown, most have adhered at least loosely to the Hayes standard. The following is a partial list of the Hayes command set. For example, M1. This is an extension of the basic command set.
Modem have small amounts of memory on-board.
Here are some of the most important characters that may appear in the modem initialization string. These characters normally should not be changed. AT tells the modem that modem commands follow. This must begin each line of commands. Ask your modem Seriously, nothing knows better than your modem which commands it accepts and how it interprets them.