VPP/RA4 voltage confusion.

[jmgelba]

Ed,
VPP is programming voltage and must be higher than 5 volts. For the 18F1320 I'm using it must be 9.0V minimum for programming mode.
RA4 was a typo and should have read RA5.

I have a space issue so I cannot use a dedicated programming header. I have to use the connector that also supplies the power, typically 15 - 42V and has the sense pins, which are either pulled to ground or pulled to the supply. Thus the programming pins on the PIC must be protected from the high voltages. All but VPP are protected by 5.0V zeners and resistors. VPP must have a 9.0V or higher zener so that it will enter programming mode when required.

Can this pin see the programming voltage when I dont want it to enter programming mode?

[Ramius]

Hi!
According to the same spec sheet you referenced earlier it states " This pin maybe kept in this range at times other than programming. But it is not recommended." Note 2 on page 254. You are talking about being able to supply a voltage at 10 ma over a wide voltage range so again I would be back to suggesting an optical isolator or 7812 unless you know the zener you plan to use will tolerate more than 10 ma. Best, Ed!