Playing with PICs on MacOS X

Introduction

Every once in a while I like playing with Microchip PIC microcontrollers. Partly this is historical: the first microcontrollers I used were PICs, but I still enjoy writing code for them and they're cheap-as-chips (plus I've already got a goodly number just lying around).

However, because this is a pleasure I enjoy quite infrequently, I sometimes forget how everything fits together, so it seemed sensible to document it.

Most of this information is available elsewhere online, both from Microchip's website¹, and from other places.²

Almost all my PIC experience uses the relatively modern 16Fxxx series of chips, which Microchip refer to as Mid-Range Core devices.

I always program in PIC assembler using the GNU toolchain, and use Microchip's PICkit 2³ programmer. There are probably other good choices, but this was the way I went.

Hardware

The PICkit 2⁴ is a handy little gadget which sits between the USB bus and a PIC. It uses the USB HID protocols, which seems to make it 'just work' as far as the Mac's concerned. Besides programming the PIC, the PICkit 2 will also supply power to the target board assuming that the current is within USB limits.

To talk to the PICkit 2, Microchip have made available a command line tool: PK2CMD. This is available in both source and binary formats on the Microchip site.

Microchip also produce a number of demo boards⁵ which are basically just a PIC, a few handy peripherals, and a small prototyping area. I've played with these so far:

• The Low Pin Count Demo Board,⁶ which includes a PIC 16F690.⁷
• The 28-pin Demo Board,⁸ which includes a PIC 16F886.⁹

Software

PK2CMD

This program talks to the PICkit2. I usually install the executables in something like /usr/local/PK2CMDv1-20MacOSX, then symlink that to /usr/local/pk2cmd. pk2cmd needs to find a file of PIC data, so you always need to supply -B/usr/local/pk2cmd.

Key pk2cmd commands include:

• Upload a hex file:

pk2cmd -B/usr/local/pk2cmd -P pic16f690 -M -F foo.hex

• Power up the target:

pk2cmd -B/usr/local/pk2cmd -P pic16f690 -T

• Power down the target:

pk2cmd -B/usr/local/pk2cmd -P pic16f690 -W

• Update the PICkit 2 firmware:

pk2cmd -D PK2V023200.hex

GNU toolchain

I use the GNU tools to assemble and link my code. As the Paint your Dragon blogger¹⁰ notes, you need to download these from the gputils page at sourceforge,¹¹ then compile and install them in the usual way:

% tar xvzf gputils-*.tar.gz
% cd gputils-*
% ./configure
% make
% make install

A sample Makefile

Once everything's installed it's just like normal. Here's a sample Makefile:

ASM_FLAGS       = -p P16F690
PK2_FLAGS       = -P PIC16F690 -B/usr/local/pk2cmd

PK2_CMD         = pk2cmd $(PK2_FLAGS)

TARGET          = flash.hex

%.hex:  %.asm
        gpasm $(ASM_FLAGS) $<

all:    $(TARGET)


test:   all upload

clean:
        rm -f *.o *.cod *.hex *.lst *.err

upload:
        $(PK2_CMD) -M -F $(TARGET)

power_up:
        $(PK2_CMD) -T

power_down:
        $(PK2_CMD) -W

.PHONY: all clean upload power_up power_down

Missing bits

Microchip provide more software for Windows users. Part of this is the MPLAB IDE which I'm happy to replace with emacs et al. On the other hand Microchip provide in-circuit debug support which has no equivalent on the Mac.

Revised by Martin Oldfield on 16 Jun 2010, original version 18 Aug 2009.
Contact: Martin Oldfield, ex-atelier@mjo.tc
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.