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MCLR connection on PIC24FJ1024GB610?

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cupoftea

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Hi,

With the MCLR pin on a PIC24FJ1024GB610 supplied by 3V3, would you ever consider connecting the MCLR with just a 2k2 in parallel with 100nF to the 3V3? Wouldn’t the 100nF be too big and deform the programming pulses?



Also, isn’t it more usual to have a 10n from MCLR to GND, and then a 10k from MCLR to 3V3?
 

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The MCLR input for most Microchip controllers has a dual purpose.

First is to provide an R-C delay after power on before the controller starts to execute code.

Second is initialize the state machine to detect In-Circuit-Serial-Programming(ICSP) start mode.

For this second purpose it is helpful to have a resistor to isolate the capacitor to ground from the MCLR input.

Note that the ICSP tool is connect to the MCLR pin of the controller and the R2 resistor isolates the influence of the C1 capacitor from the VPP/MCLR signal of the ICSP tool.

Recommended values: R1 = 10K ohm, R2 = 470 ohm, C1 = 100nF.

This Image found in data sheet DS30010074D-page 41:

1625595209077.png
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The MCLR input for most Microchip controllers has a dual purpose.

First is to provide an R-C delay after power on before the controller starts to execute code.

Second is initialize the state machine to detect In-Circuit-Serial-Programming(ICSP) start mode.

For this second purpose it is helpful to have a resistor to isolate the capacitor to ground from the MCLR input.

Note that the ICSP tool is connect to the MCLR pin of the controller and the R2 resistor isolates the influence of the C1 capacitor from the VPP/MCLR signal of the ICSP tool.

Recommended values: R1 = 10K ohm, R2 = 470 ohm, C1 = 100nF.

This Image found in data sheet DS30010074D-page 41:

1625595209077.png
 
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Althought the RC constant on this particular case is fairly small in the range of 1ms, as a general rule of thumb, regardless of its time constant, I also add an anti-parallel diode near to R1, just to ensure that a quick under-voltage disturbance on VDD would also generate negative trigger the MCLR\ pin.
 

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    cupoftea

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