{"id":1294,"date":"2011-08-09T16:00:01","date_gmt":"2011-08-09T23:00:01","guid":{"rendered":"https:\/\/www.reenigne.org\/blog\/?p=1294"},"modified":"2011-08-08T10:00:37","modified_gmt":"2011-08-08T17:00:37","slug":"a-pic12-programmer-from-an-arduino","status":"publish","type":"post","link":"https:\/\/www.reenigne.org\/blog\/a-pic12-programmer-from-an-arduino\/","title":{"rendered":"A PIC12 programmer from an Arduino"},"content":{"rendered":"

In order to program the microcontrollers for interval bars<\/a>, I needed a programmer. This is a device which connects to the chip and to a computer, and which allows one to transfer a program from the computer to the chip. You can buy them for $40 or so but I decided to make my own – since I already have an Arduino to act as a low level computer interface, I could make it very cheaply. The only complicated bit is the 13V power supply – I used this<\/a> little boost converter circuit.<\/p>\n

The Arduino program<\/a> is fairly straightforward – it just reads a hex file over the serial serial line, checks the checksums and converts it to the sequence of signals according to the PIC12’s programming specifications. It has facilities for reading back the microcontroller’s contents and passing them back to the computer as well, and also a way of calibrating the clock rate. I added this not because I accidentally overwrote the OSCCAL and backup OSCCAL values (well, I did, but I had already read them at that point so I knew what they were) but because I wanted to know what the effect of the OSCCAL value was and if the factory programmed one was optimal.<\/p>\n

I discovered that it wasn’t quite the best (the preprogrammed value of 0x24 gave a within-spec clock speed of 996.5KHz but 0x26 gave a clock speed of 1002.0KHz). I also discovered that (with the one part I tested) the low bit of the OSCCAL was ignored and the top 7 bits interpreted as a signed quantity between -64 and 63 gave an extremely linear relationship to frequencies between 587.1KHz and 1230.1KHz with a resolution of about 5KHz. I also discovered that the frequency stability was very good – a standard deviation of only about 30Hz.<\/p>\n

Here’s the schematic for the programmer:<\/p>\n

<\/p>\n

To build the programmer, edit the second line of build_programmer.bat to point to your Arduino installation (if it’s somewhere other than C:\\Program Files\\Arduino) and run it. To upload it to the Arduino you’ll need WinAVR<\/a>, modify upload.bat to point to your WinAVR installation and run it. We can’t use the avrdude from the Arduino installation here because it won’t toggle the line to reset (that’s normally done by the Arduino software).<\/p>\n

To use the programmer, connect to it with a serial monitor (like the one in the Arduino IDE). There are several one-character commands:<\/p>\n