VOGONS


First post, by foxbat

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My ATi Mach64 CT card has two jumpers described on the board as:
1. I/O JU7 (3 pin)
2. JU4 ENA INT (2 pin)

Can't really find anything about those. Only one place says something more: https://minuszerodegrees.net/manuals/Olivetti … 20computers.pdf on the last page as:

1. JU3:
I/O decode: Random
I/O decode: Block (Default)

2. Ju1
Disables the interrupt (Default)
Enables the interrupt

But what are they for? What they affect and change? What settings are for which conditions?

Reply 1 of 2, by clb

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The JU4 ENA INT pin very likely refers to the vertical refresh interrupt pin: The myth of the vertical retrace interrupt on EGA/VGA

It is a neat idea, though something that was obsoleted already from the get-go, and almost no software really uses it. Enabling it effectively causes nothing more than a micro-slowdown in CPU performance, as an unused hardware interrupt is then firing 70 times a second, continuously stealing a tiny amount of CPU cycles.

The "I/O Decode" term has been used to refer to specifying the I/O address range that the VGA adapter listens and "reacts" to, i.e. the I/O addresses that the PC should use to talk to the card. However, the options "random" and "block" seem really peculiar to me. I don't quite understand how I/O port addresses could ever be randomized that would be practically a catastrophic recipe to conflicts if that was the case. So this option it must be doing something different than that.

Reply 2 of 2, by Tiido

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The IO jumper disables VGA ports and memory range and allows the card to be a "secondary" for multi monitor operation in windows from what I remember.
Interrupt one is for VGA/EGA frame interrupt.

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