Strange memory chips on Quantum3D Obsidian (650-2200) \ VOGONS

Strange memory chips on Quantum3D Obsidian (650-2200)

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First post, by ghost.dog@mail.ru

Posted on Today, 16:33

ghost.dog@mail.ru Offline

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Posts: 8
Joined: 2023-07-21, 10:20

I recently got this card.

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It has the same 8 RAM chips as the VillageTronic MacMagic 8MB.

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But it detects only 4MB of RAM. The model number 650-2200 (2MB TMU + 2MB FBI) also confirms that it is indeed a 4MB card. Why the manufacturer used these chips instead of the usual 512KB ones is a mystery.
According to the datasheet, these RAM chips have an additional address signal on pin 15 (A9). This differs from usual 512KB chips (V53C16258HK), which have this pin unconnected (NC).
It also differs from 1MB chips (V53C819HK) typically used on late STB and PowerColor Voodoo2 cards, which have a RAS1 signal on that pin to enable two banks of 256K x 16 RAM.

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However, these chips seem to have a single bank of 512K x 16.

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The TMU chip lacks an additional address line. It has only 9 lines, but these chips require a 10th line. So, how does this work on the Mac version?
Maybe someone who owns one of these Mac cards can check where these pins are connected.

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