how can I rewrite my msx2 nms8280 bios?

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By sd_snatcher

Prophet (3068)

sd_snatcher's picture

10-09-2017, 03:10

@Grauw

I don't want to derail the topic, so I'll just post some quick answers here.

- I agree with you that if the machine has no turbo and it has an original MSX2+ BIOS, there's no need to connect the V9958 /WAIT pin
- I'm not sure if I would call CIEL homebrew. They're a small but real company, and together with DDX they sold *a lot* of products in the 80s and early 90s. I think it's not different from, let's say from the Japanese Wachi Electronics that produced the MK-Mouse II, or any smaller Japanese company that supplied peripherals. The ExpertTurbo and Expert3 are brand new complete motherboards to be installed in the Expert case, not different to the way someone installs a new ASUS motherboard in an existing PC case.
- The CIEL ExpertTurbo and CIEL Expert3 V9958 /WAIT circuit works just fine for what Yamaha stated in the datasheet: VRAM access. The problem I mentioned before is only for the register access, and the V9958 /WAIT doesn't cover that. It must be supplied by an external circuit like in Panasonic MSX2+ machines.
- All Panasonic and Sanyo MSX2+ machines have all the circuitry to connect the V9958 /WAIT circuit, so that proves that up to a point all those designs were intended to have turbos. Sanyo even used the same gate-array as Panasonic did, and the switched I/O ports answer to exactly the same ports/values. But for whatever reason Sanyo gave up on the turbo on the last minute and its gate array had the turbo clock generation part crippled.

By barman26

Supporter (6)

barman26's picture

10-09-2017, 03:20

ok. update finished.
it seems that works.
but video output voltage is low.
i can see MSX Basic version 3.0 and Disk Basic 1.0 in other words, Z80 works and VDP 9958 too.
It is necessary remove resistors R166 and R167? I find this procedure in other guide from Bas Ditta website.

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