Strange pulses on PGM pin when programming?

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

A little off-topic.
I have a PIC18F4550. The PGM pin is tied to GND via a 10k resistor. The programmer (an CCS USB ICD) is NOT connect to the PGM pin.
I am using the pin to switch off the PSU with a positive pulse, so the PIC can switch itself off!

When the ICD attempts to communicate to the PIC I see pulses on this PIN which must be coming from the PIC, this of course switches off the power!

I know PGM is associated with programming but I had assumed it is not used during high voltage programming?

Any ideas? Has anyone else seen this sort of activity?

Will Reeve · Joined: 30 Oct 2003 Posts: 209 Location: Norfolk, England

Woops my mistake it's the CLKO pin OSC2 and RA6. It appears that you get some clock pulses when you enter programming mode? I can't see where this is documented anywhere but it makes more sense than pulses on PGM! I guess I am going to swap some pins over!
It is a warning though, be careful what you connect to RA6 on these devices if you intend to ICP them.