Re: Re: Smart/Dumb box again... (CPU timing)

On 2 Mar, CAD_CAM_EDM_DRO@yahoogroups.com wrote:

> Thanks for the correction, really...!
> So, off to get my PIC burner then and join the embedded systems
> club...

Dave;

Good choice going for a genuine microcontroller. Unfortunately, a
couple of gotchas there two. ( My butt has a number of PIC shaped bite
marks, so I know whereof I speak. )

1. Don't discount the number of cycles required to save the machine
state when entering an interrupt routine and then restore things again
upon exit. It makes the PIC less fast than it seems, especially
compared to newer micros that automatically save the state ( in a
single cycle ) when entering and restore it again upon exit.

2. Note WHERE in a 4 clock instruction cycle the interrupt is
acknowledged. PRECISE timing is harder to implement as a result.
Also, it differs for different members of the family.

Now, I don't mean you should stop using PICs - I certainly haven't.
Just be aware.

Alan




--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta