[gwbas1c]

> is the same class of bug that plagued the Hayes +++ escape sequence in data mode, and it is striking that it was never properly solved.

When I ran a BBS, it was critical to configure the modem and software to use signaling lines (I forget the term's name, something like the rx or tx line) to signal commands.

I'm surprised that voice modems weren't using these, as they were common with external modems.

[dfe]

It was drop DTR. Most current documentation tells you that dropping DTR means the modem should hang up. That was an option, maybe even the default. But you could AT&D1 to make dropping DTR return you from data mode to command mode. It's so important there's even a DIP switch on the USR Courier to enable this mode.

https://support.usr.com/support/3453b/3453b-crg/chap%208-con...

I almost can't believe the USR site is still up. This is something I remember doing to run a BBS over 30 years ago. I still have my Courier with the brass not for resale plate.