Last night at HSB we had a JTAG finder workshop, during which we quickly hacked together a JTAG scanner for the ATmega328, called Arduinull (it’s not a port of Hunz’s JTAG finder as we initially planned to do). It is compatible with Arduino Duemilanove, so that people from low-standard DIY websites for the masses will see it and go “wow!”.
You can download the files here. They are public domain ; copyright is irrelevant on such a trivial piece of software. It tries every JTAG pinout on the 6-pin port C of the microcontroller analog input connector of the Arduino, shifts a pattern into the IR chain and tries to read it back. Add protective 330 ohm resistors in series with your device.
A possible improvement would be to add a relay controlled by the AVR microcontroller Arduino to power-cycle the device, in case the JTAG chip gets confused. Also, it should detect the IR length and reject a length of zero which is more likely due to two pins connected together.
I have continued my trip and I’m now at Das Labor in Bochum.
#1 by plasma on January 7, 2010 - 3:31 pm
Why do you use 330 ohms resistors? Is it to lower down the potential voltage that there is on some pins?
#2 by jal2 on March 25, 2010 - 9:37 pm
@plasma: I guess the resistors should limit the current if both side are output pins on different levels. In all other cases there will be (almost) no current, hence no voltage drop over the resistor.
@lekernel
Does the JTAG finder work both with 5V and 3.3V targets?
#3 by ddwrtunico on April 29, 2010 - 4:53 am
does JTAG Finder work with an arduino diecimila? with an Atmega168.