Add Jtag Port

From NAS-Central Buffalo - The Linkstation Wiki
Jump to: navigation, search
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 open the case and 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: [1]

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>  (key, which means this pin is often removed)
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. Some software packages do not support USB cables. [2]

The OCD port on the Linkstation uses an electrical standard known as JTAG/COP. The 16-pin COP header for Freescale devices is slightly different from the TI/ARM standards. Although this is signal-level compatible with the TI/ARM standards, unfortunately the pins are in a different order on 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.

JTAG Interface Cable

Schematics and Software to build your own

Buy one

Several inexpensive options are listed below. [3]

  • 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.


  1. This also agrees with the recommended JTAG implementation as documented in Freescale MPC8241 Info, which is the CPU used for the Linkstation HG. See pages 45-46. Note that there is no guarantee that Buffalo followed this recommendation, but it appears that they did.
  2. Most of the USB implementations appear to use a version of the FT2232 chip from FTDI, so they should all be somewhat compatible.
  3. 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, (make sure the software supports your target board)