Personally I would get rid of C3, and replace D3 with a 1k resistor.
Caps between VDD and VSS is always a good idea. Without them you can get “hard to trace” cpu instabilities…
I would say 100nF close to the CPU and another 1uF or more somewhere on the board…
Thanks Errol. That would be the easest. But the need was to isolate vpp (13v) from the 5v rail when a programmer is attached is MCLR. With just a 1k resistor, 13mA will still get into the 5v rail (i.e. stepper boards) and have some unknown side effects. At least I think so, unless I am overlooking something (which is common).
The 10k pull up to VCC will limit the 13V current to 1.3ma, if it was a short to ground.
The current from 13V into the 5V rail, through 10k resistor is (13V-5V)/10000 = 0.8ma…
But there would be no existing power on the 5v rail when programmer hooked up for ICP. That is to say, no other source.
Would that not be 13/1000 = .013amps?
Either you must supply a 5V rail, or the programmer must supply 5V.
The 13V is just to tell the PIC that it must go into program mode, it doesn’t power of that voltage…
It’s 13/10000(for 10k)=0.0013A… 