Add Jtag Port

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Revision as of 15:47, 7 September 2007 by Ghopper (Talk | contribs) (Updated links to JTAG adaptor vendors. Added a note about 14-pin vs 20-pin options.)

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Sample JTAG interface cable

This document is a work in progress. It explains how to fit the internal on-chip debug (OCD) port on a Linkstation, Kuro-Box or Kuro-Box/HG to a PC interface.


You will need to solder a 2x8 pin header to the board. You also need to build or buy a JTAG interface cable.

Adding the JTAG Port

Locate the pads

The pads are labeled CN5 and can be seen just above the serial level converter (where the yellow, orange, and red wires start to split) in this photo

Connector Pin-outs

In order to use this port, you should bridge R67.

Baulab posted cable schematics, some pictures of the assembled jtag cable, and software needed.

According to and the following pins are used for a PPC COP/JTAG interface:

TDI 3 4 TRST (Neg)
HALTED 5 6 Vcc Target
TMS 9 10 ??
SRST (Neg) 11 12 Gnd (??)
HRST (Neg) 13 14 NC (key)
CKSO 15 16 Gnd
Pin Name       Description
 1  TDO        JTAG Test Data Out
 2  QACK       Not Needed
 3  TDI        JTAG Test Data In
 4  TRST       JTAG Test Reset
 5  HALTED     Not Needed 
 6  Vcc Target 1.8 – 5.0V:
               This is the target reference voltage. It indicates that the target has power and it is also used
               to create the logic-level reference for the input comparators. It also controls the output logic
               levels to the target. It is normally fed from Vdd I/O on the target board.
               3.0 – 5.0V:
               This input is used to detect if the target is powered up. If there is a current
               limiting resistor between this pin and the target Vdd, it should be 100 Ohm or less.
 7  TCK        JTAG Test Clock
 8  CKSI       Not Connected ??
 9  TMS        JTAG Test Mode Select
10  <reseved>
11  SRESET     Soft-Reset
12  GROUND     System Ground
13  HRESET     Hard-Reset
14  <reseved>
15  CKSO       Not Connected on the 8421
16  GROUND     System Ground

On-Chip Debug (OCD) connector

Technically, JTAG refers only to the 5 pins with JTAG in the description above (wikipedia). There is a 14-pin JTAG interface, commonly referred to as the TI standard. There is also a 20-pin JTAG interface, commonly referred to as the ARM standard. For connecting to your PC, there are two common options: parallel port and USB. USB version are faster, but can also be more expensive.

The OCD port on the Linkstation uses an electrical standard known as JTAG/COP. Although this is signal-level compatible with the TI/ARM standards, unfortunately the pins are in a different orderon the Linkstation. Therefore, you will need to build your own cable, or use some wires to manually connect the proper pins. The signals have to be buffered to protect the hardware from damage and we use a JTAG adapter (such as the Wiggler™) to do this. Those with some electronics experience could build their own circuit, but there are also several inexpensive vendors.

Schematics and Software to build your own

Buy one

  • Macraigor
  • Olimex (look for a local distributor to save on shipping)
  • Amontech
  • eBay
    • A quick search on ebay will find many buffered JTAG cables for less than $20.

(There are more expensive options. I didn't include any options which are more expensive than the Linkstation. Please also pay attention to the included software, or get one that is supported by OpenOCD.)

(Most of the USB implementations appear to use a version of the FT2232 chip, so they should all be somewhat compatible.)