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I know this is a very old thread, but technically the 18F4550 and family
DO have a maximum time parameter: P17, MCLR fall to VDD fall, max 100ns.
See DS39622.

Actually, I wanted to add one other (potentially more serious, but also
maybe weirder) comment: our primary complaint is that we only have USB
ports to work with. Well, ignoring the other complaint about
platform-specific software, how about this: doesn't the USB
specification require that a particular USB port can have its power
switched on or off under software control? Why not use the USB +5V
supply line as a twiddle pin? It would need a kernel-mode driver, sure,
 but it could work (unless I'm quite mistaken about that part of the
specification - I thought you had to enable power to only one port at a
time in order to give a device an address before bringing another
unconfigured device onto the bus).

Chris

Olin Lathrop wrote:

> Tomas Larsson wrote:
>> You need precise timing (at least sort of) if you are supposed to
>> program a PIC.
> 
> No, you don't.  You only need to guarantee minimum timing.  If you know of a
> contrary case, please point out the specific passage in a programming spec.


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