Embed Notice

The #Hayes #Smartmodem had a separate data mode (in which bytes are sent/received over the phone line) and command mode (in which the computer sent commands to the modem itself).

Switching from command to data mode was simple: send the command `ATO`.

The reverse was more complicated. The modem would switch from data mode to command mode whenever the computer tried to send the special character sequence `+++`, with a delay before and after the sequence.

1/

#RS232 #modem #retrocomputing