I am new to arm and have the Atmel Kit and the Olimex boards.
I also have 2 JTAG programmers, CrossConnect USB & Spark funs JTAG Programmer/Debugger for ARM processors device which I think is called a wiggler ???
in any event, I am wondering why all these AT91SAM7S boards that I see comes with the 20 pin header. when really only a few pins are used off the JTAG device. most of the other pins are grounded or pulled to to power through resistors or directly. why is this not just done in the JTAG device and a smaller header placed on the boards ?
The interface was defined by ARM, they might have wanted to screen each signal with its own ground, for high-speed operation. Also, one or two additional signals are sometimes used.
Yes Leon is correct. The Grounds stop the cross talk so allowing faster comms.
ARM have now added SWD capability to there latest products. This stands for Single Wire Dubugging. It actaully needs 3 wires those being Ground, Clock and Data. So it is a bit like I2C in concept, and not far away from Microchip’s ICD system. It can run up to 6Mhz from what I have seen
The clever thing is that SWD is still based on JTAG so existing tools should be able to be modified. I am trying to get the full data out of ARM but it is like trying to get blood out of a stone !