> Can anyone tell me why RA4 is an "open drain" output when all the other
> PORTA pins are "full output drivers"?  It took me a while to figure that
one
> out, for a while I thought I had configured timer0 wrong.

The 'normal' PIC pins have a protection diode to Vcc, so you can not use 'm
to switch a voltage greater than Vcc. (not even using a simulated open-drain
by switching the direction). So with such a pin it would not be possible for
me to create my programmer (which switches the Vpp using a PIC pin - RA4 of
course). So uChip included - for my joy - one pin without the upper
protection diode, that can withstand a voltage up to 14V. I guess the upper
driver FET would not like being reverse-biased, so they had to make it open
drain. In't it great that I had such an impact even before I knew what a PIC
was?

Wouter

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