piclist 2001\03\14\091131a >
Thread: Questions about PIC in-circuit programming
face BY : mike@whitewing.co.uk

On Wed, 14 Mar 2001 04:14:57 -0800, you wrote:

>I have questions relating to in-circuit programming for the PIC16F77.
>* From what I understand the VPP pin must be tied to 12VDC+ during programming.
>How do I isolate the VDD pins from this high voltage?
By not connecting MCLR to VDD !
>Is it recommended to use a diode between the VDD pin and VPP pin? No
>Or should I use a resistor? Yes, if you would otherwise be connecting MCLR/Vpp to Vdd
>If a resistor is recommended, what value is recommended? Needs to be low enough to not cause spurious noise to cause a reset,
and high enough not to load the programmer. 10K would be a good guess.
>* Do I need to power the PIC with +5VDC while it is being programmed (VDD, VSS pins)?
>* When a PIC is in program mode (+12VDC on the VPP pin), what is the state of the I/O

>pins. High impedance or output low?
High Impedance
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In reply to: <000801c0ac80$650399a0$39c6ce3f@gandler>
See also: www.piclist.com/techref/microchip/devprogs.htm?key=programming
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