[Coco] What happens if a slow 6809EP is used....

[jdaggett at gate.net]

On 18 Jan 2010 at 21:29, George Ramsower wrote:

> If it is used at double speed. Does it crash?
> 
> 
>  George
> 

George 

Since the internal circuitry is actually digital in nature what becomes a major limiting factor is 
heat built up in the chip. The MC6809e is built on the logic of the MC6800 and there is 
essentially three internal timings that exist in the chip. What will eventually happen is one or 
more of these timing constraints will overlap and an instruction will not perform as specified. 

The MC6809 uses the Q clock to do internal timing and movement of data within the chip. 
The E clock is used to synchronize with the outside world in the manner of clocking data in 
and out. The third clock inside the chip is, I believe, an inverted E clock. What ends up 
happing is the rise and fall times become a major issue when increasing clock speed. 

So basically you increase the clock speed untill instructions do not operate as intended. That 
will be the fastest the chip will run at. One last note. Heat will effect rise and fall times. And 
everything inside the chip is timing dependant. 

james