Re: DMA successes with Verilog

Den Fri, 15 Jun 2018 03:08:58 +0300 skrev Nejat Dilek
<imruon@gmail.com>:
> I thought there were different outputs for NMI and IRQ from the
> peripheral chip. It makes sense since c64 make use of two and use 1
> for irq and use another for nmi. If there were two interrupt outputs
> the design somewhat would be different too.

This is btw inherited from VIC-20 which also has two identical I/O
chips (but in that case 6522 VIA) and one feeds NMI and the other IRQ.

> Completely off topic, can other hardware connected to the NMI line
> drive it high when pulled low by the CIA chip without damaging the
> chips connected to that open drain circuit. (I'm mostly a digital guy
> and suck at analog electronics)
> If it was possible though freezer cartridges might have utilized this.

It's a bad thing to drive things that way. You'd drive it out of the
spec for what the CIA can handle.


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