MCLR Line for ICSP programming the 18F8722

[sandy wilson]

Hello,

Maybe some body can help me with this. It is not strictly CCS programming but any help greatfully received.

When using ICSP should the MCLR line be connected to the Power On Reset RC circuit by a diode or a resistor. If you look at the info on Microchips site for ICSP it says to use a diode. If you look at the data sheet for the 18F8722 it says to use a resistor in the range 1k - 10k.

Any suggestions?

Thanks in advance sandyw.

[FvM]

Hello,

I've seen some applications circuit with diodes, that won't generate a power-on reset. They are erroneous to my opinion. MCLR is either high-Z or has a weak pull-up, depending on the device family. Your circuit should be able to provide a power on-reset under these conditions and accept 12V at this pin from the ICSP adapter without drawing much current. Many PICs have an internal reset timer and don't need a RC circuit at the MCLR pin. It may be used however at these parts with an external supply voltage monitor/reset device or a manual reset switch.

Regards
Frank

[PCM programmer]

You didn't say which programmer you're using.

Microchip ICD2:
http://ww1.microchip.com/downloads/en/DeviceDoc/51265e.pdf
Look at the diagrams and text on the right side. They show what to do,
and what not to do.

For CCS, look at their schematic of how to connect the ICD to the PIC:
http://www.ccsinfo.com/faq.php?page=icd_connection


Note that ICD2 uses a 10K pullup, but CCS wants a 47K pullup.

[sandy wilson]

Thanks for the help.
It was just what I was looking for.

Now back to the drawing board.


Sandyw