Connecting a spartan2 FPGA to an ISA bus

Google is your friend. You need to pay attention to whether their voltage levels are compatible. My

vax, 9000

Apart from the fact that ISA signals are 5V and I hope you have already addressed that, I can remember these points (it's been years since my last ISA design with and FPGA...)

-Pulse Polarity: You should send a Positive voltage for the interrupt

-Pulse length: There is no minimum or maximum!! You should keep the IRQ high till you recieve the acknowlege from the interrupt handler. But there is no interrupt acknowlege line on ISA!? So in practice, you should use something like a D flip-flop and connect the output to the IRQ line. When you reach the interrupt routine, the software should write to a port to clear this flip-flop using its asyc reset (or sync reset: the one that is simpler for you). Now, you may ask how on earth would it be possible to share the same interrupt line between different cards? but the answer would be a long story....

Best Regards Arash

Arash Salarian wrote: (snip regarding ISA interface)

I thought ISA was edge triggered, which is the reason it is hard to share IRQ lines. Newer ones are level triggered so that the request will stay after the first is serviced, and be processed later.

-- glen

Actually you can change the trigger the behavior of the ISA interrupts (to level or edge) by programming the 8259 interrupt controller chip on the motherboard and intrestingly, by default it is programmed differently on different operating systems! I could only assum the OP was about using the ISA card with windows that normally sets the trigger to level for the ISA bus.

Regards Arash