One simple diagnostic tool that can be adapted to a microcontroller board design for debugging this type of problem is shown at the following links:

http://www.elstonsystems.com/products/dual_20/
http://www.darkwire.com.au/html/lapt..._card.html



These are normally used as the POST CODE capture device on certain laptop computers that still have parallel ports. The DB25 connector is easy to adapt for connection to some port pins on your microcontroller. The USB connector on these is used simply for supplying 5V power to the module. You can hack up a normal USB cable and get the 5V from any power supply or battery back.

These work by simply sensing for stable changes in the 8-bits present on the pins 2 to 9 of the DB25 connector. The onboard hardware of the module captures the 8-bits and displays it on the HEX read out display. As the capture is in progress the second pair of hex displays shows the previous capture code whilst the most recent is displayed on the first pair of displays. The MCU on the ones I have can capture up to 99 separate 8-bit codes and keeps them in an internal memory for later review via the on board next/prev buttons. Due to the nature of how these work there is a limit to how fast of stable code changes that these can capture. I have not characterized the update capability rate of the one I have but have found that I can easily sprinkle progress debug codes in various places in my code and see the codes as they appear.

The ones of these that I've looked at actually use an Atmel 8051/52 style of MCU. If one wanted to get all into it you could remove the MCU and replace it with one containing your own code to change the behavior of how the capture / display worked.

Anyway ... a clever way to add a simple temporary code sequence trap to your hardware to support just the type of watchdog debug being talked about here.

To get your own check out eBay. There are multiple sellers with various models of these available. Prices vary but are reasonable.

Michael Karas