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A comment on The 6502 microprocessor is 35 years old as of September 16th. Parent comment

Re:The 6502 microprocessor is 35 years old as of September 16th by jonsen on Friday September 17, 2010 @08:28AM (#1700869)
Perhaps the most satisfying hack I ever did was with the 6809. Making it handle high speed communications directly. It was done by decoupling its address bus during instruction fetch and then feeding it instructions from a separate ROM. The effect was to let external logic handle the control flow even if the 6809 did the data processing.
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Re:The 6502 microprocessor is 35 years old as of September 16th by jacquesm on Friday September 17, 2010 @09:44AM (#1701101)
That sounds like a ROM driven bus master to me, how did you manage to get the 6809 to disenage? Using DMA/BREQ ?
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Re:The 6502 microprocessor is 35 years old as of September 16th by jonsen on Friday September 17, 2010 @10:04AM (#1701153)
NMI to let the active process save its state. Then the busses were taken over during instruction fetch. Feeding NOPs when nothing to do and appropriate instructions when needed. No jumps nor branches. Just the essential processing. A normal interrupt routine couldn't have a tight loop fast enough, so control flow was handled in parallel externally in programmable logic.
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Re:The 6502 microprocessor is 35 years old as of September 16th by jacquesm on Friday September 17, 2010 @10:20AM (#1701196)
Very cool, I highly doubt anybody will ever fully appreciate what a neat hack that is. So you basically divorced the busses from the CPU for a while making it run in a little parallel universe of it's own.

A total perspective vortex of a sort ;)

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Re:The 6502 microprocessor is 35 years old as of September 16th by jonsen on Friday September 17, 2010 @10:34AM (#1701260)
I realize it would take some more to clearly explain the intricacies, but I see you got it :-)
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