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I have a PICkit 3 with a "PICkit 44-Pin Demo Board". To get the demo board to function I need to either disable the MCLR (#pragma config MCLRE = OFF) or put a pull up on the pin, as the PICkit leaves it floating unless in debug mode.

Is there a way of getting the PICkit to drive this pin high? Do I have a faulty PICkit (got it second hand) as I don't see anything about having to use a pull up in the demo board manual?

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checking the PICKIT 3 user manual you can see the output circuitry of MCLR_ pin of the PICKIT3:

output circuitry

From the schematic, it is clear that MCLR can be driven low (by Q7) or driven to VPP (programming voltage which is can swing from 1.8 to 14V supplied by the charge pump). In theory, this circuit can drive MCLR to external Vdd, but I would expect a totally different and simpler circuit to do so if intended. This circuit is not intended to do so.

Returning to your question and as you can see from the schematic, if your PICKIT 3 can program the device(means it can supply VPP) then there is nothing wrong with your programmer. You should connect an external resistor to drive MCLR high.

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The 44 pin demo board is designed to be used with MCLR off as you can see in the Hello World example. If you want the board to work in any other way it is up to you to implement it.

The thinking is that it's easier to add a simple resistor using the prototyping or through hole areas than it is to modify and disable an existing reset circuit.

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