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For Phasor (native/Echo+ modes) improve support for null AY chip-select case

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This commit is contained in:
tomcw 2023-02-28 20:42:53 +00:00
parent a57bb0cb6a
commit db44b15c37
1 changed files with 3 additions and 1 deletions
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4
source/Mockingboard.cpp
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@ -216,7 +216,9 @@ void MockingboardCard::WriteToORB(BYTE subunit)
if (nAY_CS == 0) if (nAY_CS == 0)
{ {
SY6522& r6522 = m_MBSubUnit[subunit].sy6522; SY6522& r6522 = m_MBSubUnit[subunit].sy6522;
r6522.SetRegORA(r6522.GetReg(SY6522::rDDRA) ^ 0xff); // direction '0' = input, and empirically it floats high (so DDRA=0x00 will read 0xFF as input) BYTE ora = r6522.GetReg(SY6522::rORA);
ora |= r6522.GetReg(SY6522::rDDRA) ^ 0xff; // for any DDRA bits set as input (logical 0), then set them in ORA
r6522.SetRegORA(ora); // empirically bus floats high (or pull-up?) if no AY chip-selected (so DDRA=0x00 will read 0xFF as input)
} }
} }
else else