stef mientki wrote:
> With external programming you need a minimum amount of time according
> to the specs,
> with internal write the timing is done in the PIC, which I expect to
> be smaller ??

Sometimes the "self-timed write" mode is slower than the externally timed
write mode.  This is probably due to process variations that force the
internal timer to produce the minimum guaranteed write time accross all
variations.  External timing can be based on the controllers oscillator
crystal, which needs to slop to guarantee the minimum value.

Of course there are isues with that too.  For example all my programmers
divide the crystal oscillator down into much slower clock ticks.  The
EasyProg and ProProg use 200uS ticks, and the USBProg 83uS ticks.  Since the
ticks are asynchronous to the programming code, the software first has to
round up to the number of whole tick intervals required to guarantee the
minimum wait time, then add 1 elapsed tick to count to guarantee that number
of intervals.  For example, a 1.1mS wait requires 6 whole 200uS tick
intervals, so the firmware is told to wait for 7 ticks to elapse.  That will
cause the wait to be from 1.2mS to 1.4mS with 1.3mS being the average.  With
its shorter tick interval, the USBProg has less of this slop overhead.  It
would be instructed to wait for 15 ticks to elapse to wait 1.1mS, which
would average to 1.2mS.


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