Thanks everyone for the replies. I'll pass these comments about
Windoze on to my client. He does have an existing product
working though, driving the valves directly from an ISA card. Makes
me wonder how good it actually works. I can see that variations of
several milliseconds would cause imperfect operation of the
machine.

I know that a solenoid valve won't respond in 250us, but I guess the
idea we are working on here is trying to keep all the variables at
least one order of magnitude below that where they start causing
concern. I'll ask a few more questions.

The EPP port looks quite cool now (a bit scary at first), lots of good
web sites around for info. At first look the PSP port doesn't seem
to have the right kind of logic to make it suitable for this use. I
wondered about just an 8 bit port and an interrupt line, but I'm not
sure if handling nested interrupts is feasible on the PIC (eg.
allowing for EPP interrupt to occur during a timer interrupt or MSSP
interrupt). I'll persist with the PSP a bit more.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brown@clear.net.nz

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