(Topic ID: 261103)

Stern Galaxy code disassembly/Modifications

By slochar

4 years ago


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  • 175 posts
  • 22 Pinsiders participating
  • Latest reply 1 year ago by slochar
  • Topic is favorited by 37 Pinsiders

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  • Galaxy Stern Electronics, 1980

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#83 4 years ago

Surprised they use a 'check if game active' check on every single switch handler vs just a single bit in the matrix somewhere, or even just special casing the limited switches that matter in game over

#85 4 years ago
Quoted from slochar:

IIRC Stars and other really early sterns only react to one column in game over.... might be thinking of early Bally, though

Dracula has that, at least. Seemed nice and simple

1 week later
#107 4 years ago
Quoted from slochar:

It's 866 Khz, the 6800 they used was a 1 MHz part, but only williams at the time used it at 1 Mhz

Always wondered about that; any idea why bally+stern were slower? It seems especially weird for bally to leave theirs at <500KHz when the same board can be run at double speed for MPU-200

1 year later
#136 2 years ago
Quoted from slochar:

There is a bug in the way the 6800/6802/6808 processors handle flags concerning the X register, specifically for comparisons that would be greater or less than some value. Don't trust the results for this, but for zero/nonzero, (or equals/not equals), it's fine. Just don't expect to do a cpx #$something and then a bhi somewhere - results aren't guaranteed.

I've run into this before pinmame does the calculation correctly, but actual hardware doesn't. Very fun crash to track down. The official docs for the 6800 assembly specifically day not to use cpx for anything besides beq/bne

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