From: Spiro Trikaliotis (trik-news_at_gmx.de)
Date: 2003-10-08 21:19:37
Hello,
I'm just forwarding this question to the cbm-hackers mailing list, as there
are some people who might know more about this.
For the persons on cbm-hackers: This person wants to connect something to
the parallel port of the PC, using it as an input. He is afraid the parallel
port could be damaged while the port is put into output mode, but the
external hardware is connected.
I suggested to him using only the 4 "permanent" input bits. This was his
reply (and I include my reply to him, too):
(since I don't know if he would agree, I don't include his name here)
On Mon, Oct 06, 2003 at 09:33:52PM +0300, you wrote:
>
> Hi,
>
> Thank you very much for responding.
>
> I know about the 4-bit transfers, but I would like to use the full potential
> of my parallel port, thus a bidirectional 8-bit transfer. The protocol that
> is going to be used is custom made and therefore I don't mind about ECP and
> EPP transfers. Finaly, always assuming the worst, I do not want to rely on
> software just to avoid the hazardous condition.
>
> There must be a way to protect the parallel port using simple components. A
> 6K8 resistor in series with each data line solves the overcurrent problem,
> but rises the voltage of logic-0 higher than the TTL standard of 0V8. A
> smaller resistor would solve the voltage problem, but I am not sure if it
> would provide enough protection from overcurrents. Do you know what is the
> maximum sourcing and sinking current of the parallel port?
I'm sorry, I don't know about these. In fact, I never tried it this way, I
always connected anything without precautions, and I was lucky there were
never any damages.
I think the maximum sourcing und sinking current of the parallel port is not
really defined, as there are many different implementations of these beasts
around.
Anyway, I hope someone on cbm-hackers can help us out?
Spiro.
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