Joint Test Action Group

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Joint Test Action Group

(architecture, body, electronics, integrated circuit, standards, testing)
(JTAG, or "IEEE Standard 1149.1") A standard specifying how to control and monitor the pins of compliant devices on a printed circuit board.

Each device has four JTAG control lines. There is a common reset (TRST) and clock (TCLK). The data line daisy chains one device's TDO pin to the TDI pin on the next device.

The protocol contains commands to read and set the values of the pins (and, optionally internal registers) of devices. This is called "boundary scanning". The protocol makes board testing easier as signals that are not visible at the board connector may be read and set.

The protocol also allows the testing of equipment, connected to the JTAG port, to identify components on the board (by reading the device identification register) and to control and monitor the device's outputs.

JTAG is not used during normal operation of a board.

JTAG Technologies B.V..

Boundary Scan/JTAG Technical Information - Xilinx, Inc..

Java API for Boundary Scan FAQs - Xilinx Inc..

JTAG Boundary-Scan Test Products - Corelis, Inc..

"Logic analyzers stamping out bugs at the cutting edge", EDN Access, 1997-04-10.

IEEE 1149.1 Device Architecture - Boundary-Scan Tutorial from ASSET InterTech, Inc..

"Application-Specific Integrated Circuits", Michael John Sebatian Smith, published Addison-Wesley - Design Automation Cafe.

Software Debug options on ASIC cores - Embedded Systems Programming Archive.

Designing for On-Board Programming Using the IEEE 1149.1.

Built-In Self-Test Using Boundary Scan by Texas Instruments - EDTN Network.
This article is provided by FOLDOC - Free Online Dictionary of Computing (
References in periodicals archive ?
The 1149 standard has the formal name, "IEEE Standard Test Access Port and Boundary Scan Architecture." Engineers often refer to it as simply "boundary scan" or "JTAG"; the latter stands for Joint Test Action Group, the group that launched the standardization effort.
That's when an ad hoc working group, the Joint Test Action Group (hence the JTAG name for the methodology), began working on concepts for a circuit board test technology that would not require physical contact between a probe and a circuit board.
From humble beginnings in 1990 targeted at solving the limited-access problems of traditional board test based on a physical-touch technology such as bed-of-nails and flying probe systems, IEEE 1149.1 boundary scan applications have expanded beyond the wildest imaginations of the original members of the Joint Test Action Group (JTAG).

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