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From: marjakan@efa.cc.lut.fi (Erkka Marjakangas)
Subject: Re: bidirectional parallel port
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Date: Tue, 14 Mar 1995 15:27:18 GMT
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jmh@vttoulu.tko.vtt.fi (Jorg-Michael Hasemann) writes:

>Hello,
>I would like to get some information about the (bidirectional)
>parallel port. I know that the standard printer port is uni-
>directional only. However, newer printer port more and more
>often support bidirectional modes, i.e. writing *and* reading
>from pins D(0)-D(7).
Hmm, I never knew that. All the printer ports I've bumped to have been
bidirectional.

>My question is now, how to test whether my printer card supports
>a bidirectional printer port (e.g. PS/2 mode printer port) and
>how to actually read data from the printer port.
If you don't have specs or tech.ref. manuals there's no way to test.
Bidirectional ports quite surely have a register to indicate the direction
of each data pin. If you don't know the registers address, it's no use 
testing more. Well, you could reassemble the device driver, and check how 
it is implemented, it might come up with something, but it's probably 
waste of time

>I also would love to get information about the electrical charac-
>teristics of the bidirectional printer port.
Check for MC68230. It is described in almost all of the books about 
Motorola 68000 chip that I have seen.
If you or your friend owns Amiga HArdware Reference manual, it describes 
very thoroughly the bidirectional transfer between computer and peripheral.


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