----- Original Message ----- 
From: "Michael Curtis" <lists@moltenmercury.org>
Subject: Re: [PIC] PIC no longer wants to program - is it blown?

> prog84 will then talk to it.  As these programs previously worked, I'm
> guessing that these two are allowing my program to briefly start* before
> going into program mode, which causes the hardware to act "strange".  Is 
> this
> even possible?  I'll test by reflashing the chip tomorrow but it's late

If your program uses RB6/RB7 as outputs, a programmer (or capacitance on PGM 
or !MCLR) which allows the program to run long enough to get the port 
initialized will prevent the part from being programmed.

In HVP, this is the reason for the requirement on the risetime on !MCLR. 
The pin needs to go from Vss to Vpp without spending any significant amount 
of time around Vdd.  With LVP, it has to do with the timing between !MCLR 
and PGM, which is a little messier.  If you set the power up timer on you 
get a little more elbow room here (the next time you program!).  But 
basically, you need to get PGM high before !MCLR has spent more than a few 
of clocks around Vdd.  If the chip already has the power up timer enabled, 
you get a few clocks plus 72 ms.

--McD

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