2.5 COM Enumerator Recognition by Other COM Devices

Serial devices other than modems could respond to the COM Enumerator with a simple state machine, particularly if they don't have the modem problem of using DTR and RTS for other meanings. In this case, the timing measurement can be omitted.

On power up, set DSR=1 IDLE state (b-e).
Check for new commands, external events, internal events, RTS, and DTR.
If PC commands received, go execute commands.
If events occur, process events (reports, actions, etc).
If (DTR=0 & RTS=0) (unplugged or computer off or computer rebooted) and IDLE (e.g. not executing a command).
wait (forever) for DTR=1
COM Enumerator detection (f-h)
IF DTR=1, check RTS (h).
IF DTR=0, go back to IDLE (b).
IF RTS=1, go send COM ID (e.g., Table 4) go to IDLE (b).