Another successful afternoon where I launched Windows XP SP3 inside Parallels Desktop v3.0 for Mac, and connected to my MPLAB ICD2 PIC programmer. Yes, Wow!

I managed to test some of the code I had prepared to run the PIC18F1330 which has 6 PWM outputs, 3 independent. This will be sending the PWM signals to the motor driver, based on the instructions received over the serial link from the robot’s on-board computer.

This is where CRC comes in! The code was compiled under Hi-Tech’s PICC18 STD compiler, which I really like. It also includes routines for serial communications and the ‘direct’ CRC-CCITT method as the look-up table is far to big (and tedious) to squeeze into the available ROM.

I do not want to corner myself this early into the project by using up all the available ROM space just to store the CRC look-up table. It is great that the code is still only occupying less than 20% of available memory!

The ICD2 programmer was then connected and the program was flashed.

Erasing Target Device...
...Erase Succeeded
MPLAB ICD 2 Ready
Blank Checking...
...Program Memory
.. Config Memory
...EEPROM
...User ID Memory
...Blank Check Passed
MPLAB ICD 2 Ready
Programming Target...
...Validating configuration fields
...Erasing Part
...Programming Program Memory (0x0 - 0x1FFF)
Verifying...
...Program Memory
...Verify Succeeded
Programming Configuration Bits
.. Config Memory
Verifying configuration memory...
...Verify Succeeded
...Programming succeeded
08-Jul-2008, 17:20:24

Capacitance from the breadboard was causing issues with the serial connection but I found it to be quite reliable with a baud rate of 19200. This also has an pretty decent error rate considering that the PIC is running on its internal oscillator at 8MHz. If I wanted to, this can be increased to 32MHz via the internal PLL; I will only be trying this in the lab as I believe it would be difficult to obtain 500Hz PWM signals at this frequency. I find it interesting that my calculations have been verified since I can see that the PWM port is running at ~494Hz. Not a bad approximation if you ask me xD

The PIC was connected to a FTDI FT232RL IC which is simply a USB<->RS232 IC and this output was obtained using ‘ZTerm’ which runs in OS X and is the best terminal application IMHO.

To my surprise the CRC code is running extremely quickly, and this is thanks to all the bit shifting (>> and <<’s) operations and a few XORs. Once I get all this kit back to my lab, I will be able to pull out the ’scope and take a closer look at the PWM signals as well.

Next: Test the receive interrupt and send PWM duty cycle ratios to the PIC over the serial connection with CRC error checking of data sent!