Re: Article PC-card

From: Hársfalvi, Levente (
Date: 2001-03-01 18:02:50

Hi! írta:
> Correct me if I"m wrong, but the ISA bus's only NMI line, per se, is the
> parity error line.  Since the c64 wont be generating parity (anyone got a
> parity gen circuit?), I feel it's best to leave it unhooked so the poor
> thing doesnt get an NMI on every bus access. ;)

The ISA NMI line is rather like a special IRQ line than a parity check
signal from the mainboard. Some cards actually depend on that
possibility. The Gravis Ultrasound uses NMI for Sound Blaster emulation;
sbos refuses to run if the mainboard supports no ISA NMI (or if you
disable NMI, ie. parity check on older mainboards in the setup). These
cards should indeed represent a minority - just wanted to point out that
NMI can be used for other purposes than parity check too (depends on
what you hook the NMI vector for).

Best regards,


Ps. I found a dual 16550 serial port ISA card in a garage shop
yesterday. It is built from standard chips + 2 real DIL 40 pin 16550s in
sockets, so if anyone is planning some 16550 hacks with his C64 and
can't find the chips (or they're expensive), just let me know and I'll
send some.
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