Parallel port chip & interrupts

[danielf]

I'm using the parallel port on a touch-screen PC to control part of my Hi-Fi system. But I need to be able to generate an interrupt from the ACK signal on either negative OR positive edges (the PC default is negative-only; but if it can be changed, I can change the polarity on each interrupt, to wait for the next pulse-edge [I want to measure pulse-widths]).
Can anyone tell me the port's chip type number? It will probably vary from manufacturer to manufacturer, and maybe over time too (progress!), but is probably still register-compatible with some "industry-standard" chip. If I know the chip type I can look up its data sheet to see how to program the interrupt edge polarity.
Many thanks,
Daniel

[mjc]

With out actually openning up the case and hunting down the chip, I think your best bet would be sifting through everything you can on the manuacturers website, some time the motherboard layout will either show the chip or give its number....

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mjc
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[kenja]

If you've got a touch-screen, danielf, I'm guessing your PC is not real old. Modern motherboards use "super I/O chips" (the "southbridge" of a chipset).

[danielf]

Thanks guys for your suggestions. It's typically difficult to get data on the "all-in-one" I/O chips, as they're often proprietary to the PC (board) manufacturer.

However I've gleaned from Jan Axelson's Parallel Port FAQ that the 'old' parallel port arrangement consisted of simple logic chips, and the ACK pin was simply steered (more or less) directly into the 8259 PIC when the appropriate control port bit was set. Presumably modern combined port chips simply emulate this arrangement. Looking at the 8259 specs, I see that (typical of Intel) it is inflexible in its interrupt pin polarity, working only with low to high transitions.

So it looks like I'll have to do some hardware hacking and add an XOR gate into the ACK line, flipping its second input with a port bit to invert the ACK signal prior to reaching the PIC. Messy, but isn't pushing the limits always so?

Regards,
Daniel