BigDumbDinosaur wrote:
...
All members of the 6502 family have been designed to use a wired-OR interrupt circuit, excepting WDC’s 65C22S, which has a totem-pole IRQ output and hence can’t be wired-OR without the use of a blocking diode. A better implementation has the 65C22S driving one of the inputs of an AND gate, and another input of the same gate wired-OR to the other interrupting devices in the system. The gate’s output drives the IRQB pin on the MPU—no pullup resistor required.
That's where I got confused, this actually clarifies a bit for me. I was reading the details about 65C22S and getting them mixed up with the ones I have (which are the 65C22N).
So it does look like for the variety of 65C22's that I have, I will need to use the wire-or method. This isn't a problem of course, but it's good to know.
This of course leaves me with the question of if I should wire my 16550 directly to the wire-or chain, keep it on the 65C22's CA1 pin (part of me feels weird leaving it like this), or come up with some other interrupt controller. (But that's a topic for a different thread I think)
Login
Register
FAQ
Search
