@raganwald @sre @infosec @secops #smartmodem #hayes
I didn't use an acoustic coupler like that but the lab I worked in one summer had a couple in the storage room.
I still have this from my first modem, which considering my #AuDHD is amazing.
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.
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