A bit of background : Spread over my bench at the moment are the insides of an HP11284 Data Communication Interface for the HP9830. This is a somewhat nice-for-the-time unit that does async and sync protocols, etc.. Anyway, as well as the RS232 interface to a modem, it also has an 'RS366' interface to an ACU (Automatic Calling Unit?). From what I've managed to discover so far, this is an interface for autodialers, it uses a DB25 connector, 'RS232' voltage levels (in fact the HP11284 uses 1488s and 1489s to talk to the RS366 connector). A goolge search for RS366 provided me with a pinout (which I had anyway) and brief descriptions of the signals. But I'd like more :-). In particular, does anyone know a free (or relatively cheap) more complete spec. I;d like to know the timeing of the various handshake signals, and the encoding of the 4-bit digit-to-dial lines (it's not even obvious that '0' is sent as 0000...). What would be _really_ nice would be the schematic of an old (pre-microcontorller [1]) ACU with an RS366 interface. I don't suppose anyone knows of one. ]1] Since the HP11284 dates from 1974-ish, I would guess the RS366 interface is even older, and that discrete-logic implementations of the ACU must have existed. -tony