How connect two EPP ports to "talk" between them?
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Hope this isn't too far off-topic, but maybe somebody who has actually
done something homebrew like this can give me some pointers.
I'd like to connect two PC's with EPP ports so they could "talk" to each
other (mono-directional at any instant but reversible -- probably by
passing a "token" back and forth -- and preferably NOT using interrupts
because I'll be doing most of the programming in a high-level language).
This is a one-off job and I'm not looking for elegance or portability;
I just want something to work reliably.
Maximum cable length will be be less than 10 meters, so propagation
time should be minimal.
The programming, itself, doesn't bother me, but it's how to CONNECT
the two parallel ports and how to implement half of the handshake.
Each port has the following pins/functions available:
DIRECTION: DESCRIPTION(#)
Out: Write
InOut: Data (8)
In: Interrupt
In: Wait
Out: DataStrobe
Out: Reset
Out: AdrsStrobe
In: Spare (3)
Ground: (8)
Some connections are fairly obvious:
* 8 data lines to corresponding 8 data lines
* 1 (or a few) ground line(s) to ground line(s)
* DataStrobe outputs to the other's Interrupt inputs
(but I'll DISable the Interrupts).
Possible algorithm:
Assume one PC is started as SeNDeR and the other as ReCeiVeR:
Not sure how RCVR lets SNDR know it is ready to receive,
but RCVR furiously polls the Interrupt input.
SNDR writes the data to its port.
which causes Write to go low
which causes data to be dumped on the output data lines
Not sure what signal from RCVR should be the SNDR's Wait signal.
but when SNDR's Wait is low SNDR's DataStrobe is set high
Something tells me this just isn't going to work!
I don't suppose you have TCP stacks for the two machines?
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