From: Davison, Lee (Lee.Davison_at_merlincommunications.com)
Date: 2003-10-09 00:26:47
'Lo all,
> I'm just forwarding this question to the cbm-hackers mailing list, as
there
> are some people who might know more about this.
>> There must be a way to protect the parallel port using simple components.
There is, simply connect a resistor in series with each bi-directional line
you wish to protect. A value of 180 to 220 ohms should work.
One thing to note is that this may delay the signals if you're trying to
make
high speed transfers, it may also reduce the noise immunity on longer
cables.
It may help to put the resistors all at the mostly receiving end of the
cable
or, if the data goes equally both ways, split the resistance between both
ends
of the cable. At worst this will nearly double the signal speed compared to
the
single resistor solution.
> I think the maximum sourcing und sinking current of the parallel port is
not
> really defined
There is more than one "maximum current" limit. The lowest one is usually
the
maximum that can be sourced or sunk and the output still be within the
defined
voltage limits for the logic levels for the device. This is usually only a
few
mA at best.
The next is the short circuit current that can be sourced or sunk by one
pin,
this can be a couple of hundred mA.
Lastly is the maximum current per package before you let the magic smoke
out,
this can be half an amp or so but isn't recommended as common practice.
Lee.
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