Carey Fisher - NCS wrote:
> Let me restate the question:
> 
> Why can't the ICD2 program a 16F627A when both
> the internal oscillator and internal MCLR are selected?
> 
> Thanks,
> Carey
It depends on what you do with your code vis-a-vis the port lines used 
for programming.

If your code asserts those pins (clk/data) into the "wrong" state, then 
the programmer cannot program the device.  If MCLR is available 
externally, then the programmer can control everything.  But with 
internal control of MCLR, once power is applied the code starts 
executing and if it changes the port pins, the programmer can do nothing.

All is not lost however.

If you have room and it doesn't adversely affect your project, you can 
put a delay in the beginning of your code that puts the pins in the 
preferred state then goes into a delay routine.  This is to give Vpp 
time to get established without interference from your code.  Then you 
should be able to program the device.  This is from a topic on the 
Microchip forum on this very same business.

One other enterprising person put a transistor in his programmer to 
apply Vdd only if Vpp is available.  You can see all this and more by 
going to the m'chip forum and searching on  ICDWarn0033.


Good luck!
MD
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