You remember incorrectly. "ATD" was basic "dial" command. It dialed the number in whatever was the default mode configured for the modem. OPTIONALLY, you could 'prefix' the number to be dialed with either a 'T' or a 'P' to force dialing in a particular manner. > >Also, for dialing out of a PBX, wasn't a 'pause' character needed to >allow time for the second dial tone?
That depended on the PBX. You could also do it at two separate commaneds -- e.g: ATDT9; ATDT18005551212
Entirely correct. tone dialing was ubiquitous at businesses, but did not have anywhere the same degree of penetration on residential lines. A lot of people refused to pay the extra per month charge.
Hayes was the _early_ leader in building affordable modems for the home/hobby market. they did a poor job of adapting to the changes in the marketplace, as speeds went above 2400 baud. the 'higher speed' market became fractured, as there were _not_ any standards to follow. There were a number of 'proprietary' schemes implemented -- resulting in manufactur A's high speed modem not being able to talk to manufacturer B's unit, except by falling back to 2400, or maybe 1200.
The Pac Rim 'copycat' manufacturer's came along, and were putting 'price pressure' on the lower end of the line, while 'incompatibility' problems plagued the high-end sales.
If so, it was not a genuine Hayes unit. Some of the copycat manufacturers did build in those 'shortcut' commands. In the true Hayes command set, the 'T' or 'P' was part of the 'dialed number', not part of the command. for modems that 'saved' numbers, for 'speed dial", or for 'auto-dial', the 'T' or 'P' was kept as part of the stored number. You just issued an: "AT {mumble} 4" for example, to speed-dial stored number #4, where the string stored as #4 was "T
555-1212".