NMI signal on ISA Videocard \ VOGONS

NMI signal on ISA Videocard

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First post, by Mov AX, 0xDEAD

Posted on 2026-09-16, 23:25

Mov AX, 0xDEAD Offline

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On Trident isa video card like 8900 NMI signal (ISA A1 - CHCHK#) connected to main videochip, marked pin as OUTPUT.
What purpose ?

Reply 1 of 2, by MikeSG

Posted on Yesterday, 12:04

MikeSG Offline

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It's like a parity check on the video cards RAM, or the card might output the signal to declare and unrecoverable crash. It'll halt the whole system or at least the VGA part.

Normally unused unless the card has a problem.

Reply 2 of 2, by Mov AX, 0xDEAD

Posted on Today, 12:01

Mov AX, 0xDEAD Offline

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MikeSG wrote on Yesterday, 12:04:

It's like a parity check on the video cards RAM, or the card might output the signal to declare and unrecoverable crash. It'll halt the whole system or at least the VGA part.

VideoRAM never has parity, and videochip cannot "crash", it's hardware, not software.

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