[Coco] Kip's Single Board Computer

[Dave Philipsen]

Actually, thinking about it, if it's a two-cycle instruction then the 
address would just increment once every two cycles.  The CPU only 
fetches one byte.  Two cycles later it fetches the next byte at an 
address that is just one greater than before. So you'd get address $1212 
for the first NOP, $1213 for the second NOP, etc.  A0 would oscillate at 
500 MHz for a 1 MHz clock, A1=250 MHz, etc.

Dave Philipsen



On , RETRO Innovations wrote:

>> This is correct except that NOP is actually a 2-cycle instruction.  
>> The 2nd
>> cycle of each NOP will read the following location.  The sequence of
>> addresses presented will be $1212 and $1213 for the first NOP, then 
>> $1213
>> and $1214 for the second NOP, etc..  So, following the first NOP, the
>> address bus will increment on every other CPU cycle.
> Would it really increment the address bus counter like that on the
> external pins?  6502 is a 2 cycle NOP, but the address lines do not do
> that, they just (as you note) increment at clock/2.
> 
> Jim
> 
>> 
>> - Darren
>> 
> 
> 
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