What is "JTAG" ?

[shedeed]

What is a JTAG, what it does standard for, what is its usage? and its impact on the DSP kit programming

 

[luminiscence]

JTAG is a in-system programmer and emulation protocol for certain types of micro-controllers.
If you want the JTAG interfacing for MSP430 and AVR's for instance, you can go to https://www.olimex.com/dev for the schematics and documantations for the JTAG circuits. One big advantage of JTAG is that you can actually do a "hardware" step-by-step debugging, the same way u do in software, like setting up interrupts and stuff ...

 

[ARTMehr]

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.

JTAG, an initialism 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 was standardized in 1990 as the IEEE Std. 1149.1-1990. In 1994, a supplement that contains a description of the boundary scan description language (BSDL) was added. Since then, this standard has been adopted by electronics companies all over the world. Boundary scan is nowadays mostly synonymous with JTAG.

While designed for printed circuit boards, it is nowadays primarily used for testing sub-blocks of integrated circuits, and is also useful as a mechanism for debugging embedded systems, providing a convenient "back door" into the system. When used as a debugging tool, an in-circuit emulator which in turn uses JTAG as the transport mechanism enables a programmer to access an on-chip debug module which is integrated into the CPU via JTAG. The debug module enables the programmer to debug the software of an embedded system.


:idea:

 

[smartsarath2003]

The debug module enables the programmer to debug the software of an embedded system

Hai,
I am new to JTAG Boundary scan Technique.Iam trying to implement this boundary scan on my project.
I have a Micro controller with few switches connected to its inputs and some leds on its outputs. It also has JTAG inteface. Previously I planed to flick the switch and read the particular LED is on. Now I feel I can simulate the input by writing a test vector and and read the output by reading the test pattern. Can you please tell me,weather this is possible with Boundary scanning. Also will there be any simple and basic programs avilable anywhere using any standard JTAG boundary scan software. Its just for me to get an idea of how to and where to start. :roll:

I have also red somewhere that, if few IC's were connected to the same JTAG inteface, on board connections can be checked for continuty using the boundary scan methos. How is this possible.
Can any one plese help me regarding my doubts??? :?:
Thanks in Advance
Smartsarath2003

 

[kawish]

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.