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JTAG, an acronym for Joint Test Action Group, is the usual name used for the IEEE 1149.1 standard entitled Standard Test Access Port and Boundary-Scan Architecture for test access ports used for testing printed circuit boards using boundary scan.
JTAG boundary scan started as a method of testing ICs and their interconnections using a shift register built into the chip so that inputs could be shifted in and the resulting outputs could be shifted out using only four I/O pins (clock, input data, output data, and state machine mode control). This eliminated the need for complex, expensive, bed-of-nails cards for low-speed probing of IC I/O pins.
Eventually, the uses of JTAG expanded to include things like debugging software for embedded microcontrollers, thus reducing the need for in-circuit emulators. And JTAG is a natural match for downloading configuration bitstreams to FPGAs.
The main purpose of the jtag at the time of discovering is to detect the inter connection between the extrnal world to the core logic in the chip. but now a days jtag is also using for the chip programing and results checking and all type of advanced programing in chip.
JTAG cells - also known as boundary scan cells, are small circuits placed just inside the I/O cells - he purpose is to be able to supply/capture data to/from the I/O through a kind of shift register called the boundary scan chain.
The interface to these scan chains are called the TAP (Test Access Port), and the operation of the chains and the TAP are controlled by a JTAG controller inside the chip that implements JTAG.
JTAG stands for Joint Test Action Group, the group that created the methodology - which is now IEEE standard 1149.1
Hello john generally when do we place these JTAG cells in physical design??
After completion of our design or when we do placement ?
Where do we put these Jtag cells beside the I/O pads ????If it is placed beside i/o pads that means in the core margin??
Where does this space provided ? for palcing the Jtag cells..........
Plz reply me........