Extension Konami SCC flips

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Enlighted (6844)

ARTRAG's picture

06-03-2022, 12:34

Very interesting...
@Ro let us know if you do experiments on real hw

By ro

Scribe (4698)

ro's picture

06-03-2022, 13:38


The Manuel Pazos information was key. By READING the test/deform reg, it is set to #FF in the process. When b6 (also b7) is set, you can't write to the Wave registers. That's exactly what happened. So, just by poke 0x98E0,0 it is reset and the Wave regs are writable again. Resulting in successful scc search.

The thing is, when I open the monitor for #9800 (to have a look at the wave data), it also reads the test/defrom reg(s) and that results to a scc write lock. Very annoying indeed.

Haven't tested this on real HW, only openMSX.

As every one's always pointing to Albert/Bifi's http://bifi.msxnet.org/msxnet/tech/scc page for SCC info, I think it's time to update that page. I'll contact Albert and point'm to https://github.com/openMSX/openMSX/blob/master/src/sound/SCC.cc for that last bit of information.

Thank you Manuel for pointing me in the right direction.

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