Category:JTAG

A JTAG interface is a special four/five-pin interface added to a chip, designed so that multiple chips on a board can have their JTAG lines daisy-chained together, and a test probe need only connect to a single "JTAG port" to have access to all chips on a circuit board. The connector pins are
 * 1) TDI (Test Data In)
 * 2) TDO (Test Data Out)
 * 3) TCK (Test Clock)
 * 4) TMS (Test Mode Select)
 * 5) TRST (Test ReSeT) optional.

http://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Jtag_chain.svg/300px-Jtag_chain.svg.png

In addition to the above 5 signals, you also need to connect VDD and Ground signals from the board. There are several interface cables that include all these pins and a few extra ones. The 14-pin (2x7) interface is known as the TI standard, while the 20-pin (2x10) interface is known as the ARM standard. The Linkstation HG uses a 16-pin (2x8) interface which is standard for Freescale/PPC boards.

See Add Jtag Port for a list of cable vendors.