JTAG
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The Joint Test Action Group (JTAG) standardized a 5 pin boundary-scan test port as IEEE Std. 1149.1, "Standard Test Access Port and Boundary-Scan Architecture".
While originally intended for boundary-scan testing of PCB assemblies, to replace bed-of-nails testing, the JTAG port included in many popular microprocessors is also often used for programming and debugging.
"If you have information on how to connect a JTAG probe to a Nokia phone, please let me know."
There are five pins:
- TCK/clock
- TMS/mode select
- TDI/data in
- TDO/data out
- TRST/reset (optional), when driven low, resets the internal state machine.
Except for TCK, all other JTAG lines should be pulled high via a resistor.
WARNING: unconfirmed pinout. Please add links to pinout standard.
20 Pin JTAG PinOut
Which one of these is right?
Pin Function Pin Function 1 TRST 2 GND 3 TDO 4 GND 5 TDI 6 GND 7 TMS 8 GND 9 TCK 10 GND 11 VPP_E 12 GND 13 A/W 14 GND 15 User 0 16 GND 17 Rdy/Bsy 18 GND 19 User 1 20 Vcc
1 +3.3 V 2 +3.3 V
3 nTRST 4 GND
5 TDI 6 GND
7 TMS 8 GND
9 TCK 10 GND
11 -- 12 GND
13 TDO 14 GND
15 nRST 16 GND
17 -- 18 GND
19 -- 20 GND
external links
- the OpenJTAG wiki ( http://openjtag.net/ )
- "When designing development boards what style JTAG connector should I use?" The 20-pin JTAG connector.
- "Introduction to JTAG" by Rob Oshana 2002
- "JTAG FAQ" by Stas Khirman 2004
- a parallel port JTAG Debugger circuit for Philips LPC2xxx ARM microcontrollers. by K9JTAG (uses Schmitt trigger inverters, so it can connect 3.0 V target boards to a standard 5.0 V parallel port)
- parallel port JTAG "Building Simple JTAG Cable" (resistors only)
- "JTAG Bus Description"
- Wikipedia:JTAG
- OpenWRT wiki: JTAG Cables
- the Jtag-Arm9 project at Sourceforge gives instructions and photographs of a Home made JTAG interface (also shows an example of prototyping using SMT IC)
- the JTAG protocol by Mark Whitis
- "Building AVR Jtag clone" includes schematics and firmware.
