[GreenKeys] Teletype Model 40 Printer with Windows

[jhhaynes at earthlink.net]

Well there are Model 40s and then there are Model 40s.  I believe the
earliest Model 40 had only the Teletype Standard Serial Interface, which
is an odd thing that transmits 18-bit words at high speed, serially.
Then there was a thing called the Model 40 OEM printer, and that has
a modified RS-232 interface.  You put data into it on the Receive Data
lead, and there are switches underneath the printer that set the baud
rate and some other things.  What is modified about it is that you can't
just send all the characters you want at high speed without overrunning
the printer, so there is a Ready for Next Character lead that is not
part of RS-232 but indicates the printer is ready for another character.

Computers have COM ports, which are RS-232, so you should be able to
connect one of those to the Model 40 if it is the OEM model, using
the Transmit Data lead from the computer going to the Receive Data
lead on the printer.  Run the Ready for Next Character signal back to
the Clear to Send lead in the computer.  Then you have to do some
messing with the software to get the COM port to the right speed and
get it using the Request-to-Send/Clear-to-Send protocol so that it only
sends when the printer is ready.

Then there are other varieties of Model 40 printers which have an
additional control board, usually in the stand.  Some of these are
ASCII and some are EBCDIC.  They may operate using the IBM Binary
Synchronous Communications protocol, which is something the PC COM
port probably cannot handle.  But maybe you can take the controller
off and get straight into the printer.

Then there might be some - I'm not sure about this - that are buffered
serial so as long as you don't send too fast you can send continuously
and the printer will keep up with it.  I think 2400 baud is about the
right speed for that.