Identify JTAG pinout

Development Boards MicroMod
1

Could someone point me to an empirical(if not easier) way to identify the TDI, TDO, TMS and TCK pins.

I’ve found a 2 x 10 patch on the board I’m working on and even went ahead and added a header.

|2—20|(even holes)

|1----19|(odd holes)

Pin 2 would be carrying 3.3v but its missing a diode so it has nothing.

Pins 4 through 20 (even) are ground.

Pin 1 through 7(odd) and 17 are carrying 3v.

13 is carrying ~1v.

9,11 and 19 show 0v.

I tried the standard 20 pin arm jtag pinout found here »JTAG FAQ and it is an ARM11 processor but no luck.

I scoured google for the past 3 days trying to find some way to come to an answer with my limited tools.

I came across this »ASkr's Hardware Projects but the author doesn’t go into much detail, atleast that I can understand, of what is to be derived from the readings you get. Add to that my inability to grasp terms like “pull high” and you get a sense of the pickle I’m in.

I have at my disposal a digital multimeter, a soldering iron, various resistors, a rubberband, a straw and a paperclip. Sadly those MacGyver tapes didnt help at all.

I don’t know anyone that has an oscilloscope and I’m broke as a bone so thats out of the question.

2

No way to be sure, but it certainly sounds like a standard ARM 20 pin jtag. Schematic for the LPC2148 board sparkfun sells is at

http://www.olimex.com/dev/images/lpc-p2148-sch.gif

3: TRST

5: TDI

7: TMS

9: TCK

11: RTCK

13: TDO

15: RST

I didn’t check your links yet to see if they match.

I take it your processor is BGA, or there is some other reason you can’t ohm from connector pin to IC pin?

You might want to post your processor type and any additional info you can scrape together, possibly in the ARM / LPC forum. It could be you have some pins in the wrong state at reset to enable jtag.

3

There was a nice talk about JTAG reverse engineering on the 26th CCC.

http://events.ccc.de/congress/2009/Fahr … 70.en.html

You may be interested by the paper at the end of the page.

4

With the help of a memeber from another forum I actually resolved the issue. For some reason I coudn’t get JTAG access with TRST connected so that solved that.