Officially an acronym for Joint Test Action Group, the group responsible for IEEE STD 1149.1 and IEEE STD 1149.4. However, most people use JTAG to refer to the boundary scan interface standard mentioned in the above IEEE documents. JTAG began as an interface to a serial shift register, the bits of which correspond to digital port pins on a chip. JTAG uses shift-in and shift-out signals, so that you can load a pattern for all of the devices on a PCB and read out the results. The JTAG interface has grown to support other features used in manufacture, test, and debugging. Many newer flash devices support programming loading through JTAG, and many microprocessors will allow for remote debugging via JTAG.

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