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Jtag

JTAG, or Joint Test Action Group, is standardized as IEEE 1149.1 for boundary scan testing, enabling testing and programming of devices on PCBs using a few dedicated pins. It facilitates boundary scan testing, in-system programming, debugging, and hardware bring-up. Various tools, including debuggers and boundary scan software, utilize JTAG for efficient device management and testing.

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Kaushal Tiwari
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50 views7 pages

Jtag

JTAG, or Joint Test Action Group, is standardized as IEEE 1149.1 for boundary scan testing, enabling testing and programming of devices on PCBs using a few dedicated pins. It facilitates boundary scan testing, in-system programming, debugging, and hardware bring-up. Various tools, including debuggers and boundary scan software, utilize JTAG for efficient device management and testing.

Uploaded by

Kaushal Tiwari
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Introduction to JTAG

(Joint Test Action


Group)

Basics, Architecture, and Use Cases


6/19/2025 Justine Litto Koomthanam 1
What is JTAG?

• JTAG stands for Joint Test Action Group


• Standardized as IEEE 1149.1 for boundary scan testing
• Provides a way to test and program devices on a PCB
• Uses a small number of dedicated pins to access internal chip
functions

6/19/2025 Justine Litto Koomthanam 2


JTAG Pinout (TAP Interface)

• TCK – Test Clock


• TMS – Test Mode Select
• TDI – Test Data In
• TDO – Test Data Out
• TRST (optional) – Test Reset
These pins allow serial communication with the test logic inside
chips.

6/19/2025 Justine Litto Koomthanam 3


What Can JTAG Do?

• Boundary Scan Testing – Detect shorts, opens, stuck-at faults


• In-System Programming (ISP) – Program microcontrollers,
FPGAs, CPLDs
• Debugging – Access internal registers, set breakpoints, memory
access
• Hardware Bring-up – Verify device response and power state

6/19/2025 Justine Litto Koomthanam 4


How JTAG Works

• JTAG controller sends data via TDI to device scan chain


• Data shifted through internal registers of connected devices
• Output observed via TDO
• TCK and TMS control data flow through JTAG state machine

6/19/2025 Justine Litto Koomthanam 5


JTAG Scan
Chain
Architecture

Justine Litto Koomthanam 6/19/2025 6


Tools that Use JTAG

• Debuggers: SEGGER J-Link, Keil ULINK, ST-Link


• Boundary Scan: XJTAG, JTAG Technologies, Corelis
• FPGA Tools: Xilinx iMPACT, Intel Quartus
• Open-source: OpenOCD, CMSIS-DAP

6/19/2025 Justine Litto Koomthanam 7

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