[Coco] 6x09 read and write strobes.

[john dumas]

On 12/18/2011 8:05 PM, jdaggett at gate.net wrote:


> an inverted E-clock if Iread the schematic of the 6800 correctly. The 6809 used the same
> basic archetecture as the 6800. They reprogrammed the internal PLA for different
> instructions and added some other circuits. One was an Intruction Set Modify Register for
> which there is a patent for that. The opcodes $10 and $11 affectionately called pre-bytes
> actually modify the opcode following by changing the output of the PLA in the intruction set
> decode logic. The other main circuit added was the Fast Interupt Circuit. Again a patent was
> awarded for that. That gave the 6809 the FIRQ, a second interrupt source.
The 6809 die plots that I saw did not have a PLA for the decode logic, 
but used random logic gates.
IIRC Bryant and Dennis busted their buns cramming in the logic, 
maintaining that array logic
like PLAs would eat up too much die area. As an aside, the push to keep 
the smallest die
size was the central element of a continuing - friendly - battle between 
Terry and Joel on
one side and Bryant and Dennis on the other. ....A common tension 
between "features"
and "producibility" in those days..........
Been there, done that.... on both sides myself!

In the end , the 09 ended up like the 00, with random logic. Later 
designs went to array logic,
microcoded, etc...

cheers,
johnd