this seems like this question has an obvious answer but despite looking through the datasheet of the PIC MCU I'm going to be using (the PIC18F45K22), and the SNAP programmer user guide, I can't find the answer.

I want to program the microcontroller using this programmer, but I'm not sure what pins on the chip should connect to which pins on the SNAP. The most relevant information I can find in the user guide is the "ISCP (MCHP)" column in the "Pinouts for Debug Interfaces" table on page 38:

The table

According to this table, it would seem that if I want to program my microcontroller using ICSP (which I believe I do), I would connect pin 1 of the SNAP to MCLR, for example. This I can do. But, where it says to connect pin 6 to AUX I get confused, because nowhere in the datasheet for the microcontroller is such a pin mentioned.

ICSP (MCHP) seems to be the most relevant of all of the columns in that table, so I'm confused as to how the pins don't seem to match up with what is said in the datasheet.

  • 2
    \$\begingroup\$ 'DAT == 'PGD', 'CLK' == 'PGC', don't worry about 'AUX'. \$\endgroup\$
    – brhans
    Commented Aug 1, 2021 at 19:58
  • \$\begingroup\$ Thanks, that makes sense. So, AUX can just be disconnected? What's the point in it then? \$\endgroup\$ Commented Aug 1, 2021 at 20:13
  • \$\begingroup\$ No idea - when I worked with PICs I only ever need 5 pins connected. \$\endgroup\$
    – brhans
    Commented Aug 1, 2021 at 20:14
  • \$\begingroup\$ Huh, weird. Well, if you write that up as an answer I'll mark it as accepted :) \$\endgroup\$ Commented Aug 1, 2021 at 20:20
  • \$\begingroup\$ The AUX is for low voltage programming on selected parts so that you don't need to pull MCLR to 12V to enter programming mode \$\endgroup\$ Commented Aug 2, 2021 at 12:40

1 Answer 1


The PIC18F K series uses the old Microchip PGC/PGD, it's not a JTAG part.

You need to use the ICSP column. Don't worry about the AUX pin, it's only use in certain low-voltage programming situation as programming trigger.

The problem is that Microchip is buying everyone so it has many different controller families, each one with its own interface.


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