JTAG Cables and Programmers

JTAG is a popular serial interface used in professional embedded systems and commercial electronic devices. It is used to program, read and debug on-board electronics. Since all chips on the circuit board can be connected in a chain there is only one JTAG connector needed. Unfortunately this connector is not standardized and there are many different pinouts used. Different pinouts and different applications have resulted in many JTAG programmers for specific devices.

A popular use of JTAG cable is to program routers and Xbox devices. In fact, almost all programmable electronic devices support JTAG interface, but the connector is not always implemented. While the JTAG itself is standardized there is no universal programmer. You will have to get one for each device type you need to program.

The simplest JTAG programmer is only an interface between parallel port and JTAG. A software running on PC controls signals on parallel port which via JTAG interface control JTAG signals. A more sophisticated JTAG interface has own microcontroller and connects to PC via USB. JTAG programmers/interfaces are cheap and you can even build a simple JTAG cable!