What is JTAG and how can I make use of it?

You may be familiar with JTAG because you have used tools with a JTAG interface. Processors often use JTAG to provide access to their debug/emulation functions and all FPGAs and CPLDs use JTAG to provide access to their programming functions. JTAG is not JUST a technology for processor debug/emulation.

What kind of test equipment do I need for JTAG?

Traditional test technologies require very large and expensive equipment. The only test equipment required for JTAG / boundary scan testing is a JTAG controller – XJTAG’s XJLink2 controller is a similar size to a PC mouse.

Why do FPGAs and CPLDs use JTAG technology?

Processors often use JTAG to provide access to their debug/emulation functions and all FPGAs and CPLDs use JTAG to provide access to their programming functions. JTAG is not JUST a technology for processor debug/emulation.

Where are the cells of the JTAG Register?

As its name suggests the individual bits, or cells, of this register are at the boundary of the device, between its functional core and the pins or balls by which it is connected to a board – very often JTAG testing is referred to as boundary scan.

What can a JTAG do for a harddive?

A JTAG can do this to but can also run exciting home brew applications like emulators (Nintendo, Super Nintendo, Sega, Etc, Etc) and it allows you to play the game off a harddive without ever needing the game disc at all.

Why do you need a JTAG connection test?

A JTAG connection test will check that the connections around the JTAG enabled devices on a board are the same as those specified in the design. Where two JTAG enabled pins are meant to be connected the test will make sure one pin can be controlled by the other.

Can a JTAG state machine access an instruction register?

The JTAG state machine can reset, access an instruction register, or access data selected by the instruction register. JTAG platforms often add signals to the handful defined by the IEEE 1149.1 specification. A System Reset (SRST) signal is quite common, letting debuggers reset the whole system,…