VLB Cirrus Logic GD-5428 switches \ VOGONS

VLB Cirrus Logic GD-5428 switches

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First post, by vstrakh

Posted on 2022-07-06, 09:16

vstrakh Offline

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I've bought this card, by FCC ID lookup it's a Joytech GD26ACVL2M.

It has a single jumper switch in the corner, in the immediate vicinity of VESA connector's pins.
Judging by traces around that jumper it selects some signal to come either directly, or inverted (the MC74F04N chip nearby is inverter).
I've never had any VESA cards before, so I've no idea what was possible to select with jumpers on VLB video cards.
Any ideas what it could be?

Reply 1 of 2, by Babasha

Posted on 2022-07-06, 09:22

Babasha Offline

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Usually there two jumpers.
One for VLB 25/33MHz or 40/50MHz.
Second for 0WS or 1WS VLB Bus.

Need help? Begin with photo and model of your hardware 😉

Reply 2 of 2, by vstrakh

Posted on 2022-07-06, 10:57

vstrakh Offline

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Joined: 2021-04-09, 12:31
Location: Ukraine, Dnipro obl.

0WS would be about masking out the signal, not inverting. So it's definitely not related to WS.

Checked the continuity, the inverter input sits directly on the pad B56 - LCLK. So the jumper is about selecting the clock edge to sample other lines.
This is exactly timing related, choosing the right spot in time to sample the bus by adjusting the clock phase.
It's not the bus speed selection per se, but directly related. Thx for the hint 😀

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