Re: [openwince-list] xoscope
> I have some JTAG connectors I do not know the pinout.
> Does someone knows how to use xoscope to detect the JTAG pinout?
Target or adapter side? If you want to find out the pinout of connectors
on a target, the best starting point is to look for datasheets of all the
chips on the target; probably there are dedicated JTAG pins. Then try to
measure connectivity between those pins and the connector. If you don't
have a low-current continuity checker or ohm meter, you could instead
inject a small AC signal at one of the device JTAG pins and try to
locate it on the connector.
It's not possible to differentiate the pins using only a scope unless
you can actually watch some JTAG transfers. But as you don't know the
pinout, you probably also can't do transfers yet...
If there is no device on the target with known JTAG pins or it is
something like a BGA with all connections hidden underneath,
1. find a pin on the connector with obvious connection to ground plane
2. find the logic voltage level (often there's at least one pin at high
level when the device is powered)
3. find out which other pins are connected to something beside GND or
VCC (looking at the PCB helps most)
Then assuming that you already have a JTAG adapter that supports the target's
4. try all possible permutations of the four JTAG signals on those
connected pins. With series resistors of about 100..500 ohms and low
JTAG clock, you very probably won't damage anything.
Actually, I've seen only very few boards where JTAG connector was
different from the standard pinout of the JTAG cable for the major
component on the board (usually the CPU). Only tight space sometimes
makes developers use nonstandard connectors.
- From: Benjamin Henrion <email@example.com>