V9938 16K?

By Eugeny_Brychkov

Paragon (1232)

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06-10-2010, 23:19

Hi guys, I have made 64K module for V9938 using 64Kbyte SRAM. Machine is CX7M (MSX1-64K-V9938 "YIS503II" - you can see schematics on msxblue).
Problem is that TESTRAM.COM shows only 16K (like with regular 16K DRAM video board). What could be the problem? Can MSX1 BIOS be a limitation for TESTRAM?

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By Eugeny_Brychkov

Paragon (1232)

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06-10-2010, 23:44

Ah I seem to have mixed address lines to the memory chip! That's not so straightforward like A0-A0 .. A7-A7! Need to make some experiments...

By Eugeny_Brychkov

Paragon (1232)

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07-10-2010, 10:28

That's BIOS problem. VDP mode register #8. To access more than 16K bit 3 (VR) should be 1. Bios always keeps it 0. When I set it to 1, I can access whole 64K of the SRAM chip. I need to find MSX2 machine (YIS503III) to continue experimenting.

By mohai

Paladin (999)

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07-10-2010, 16:11

Where are those schematics exactly?
I did not find them in msxblue.com