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JTag On Off

The document provides an overview of the JTAG (Joint Test Action Group) interface, which is standardized as IEEE 1149.1 and primarily used for debugging embedded systems, in-system programming, and boundary scan testing. It details the historical context, pinout, applications, and comparisons with SWD (Serial Wire Debug), highlighting its significance in modern embedded systems, particularly with ARM Cortex-M MCUs. Additionally, it discusses advanced JTAG uses and tools for implementation, emphasizing its role in efficient debugging and programming of devices.

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SAI SIVASANKAR
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9 views11 pages

JTag On Off

The document provides an overview of the JTAG (Joint Test Action Group) interface, which is standardized as IEEE 1149.1 and primarily used for debugging embedded systems, in-system programming, and boundary scan testing. It details the historical context, pinout, applications, and comparisons with SWD (Serial Wire Debug), highlighting its significance in modern embedded systems, particularly with ARM Cortex-M MCUs. Additionally, it discusses advanced JTAG uses and tools for implementation, emphasizing its role in efficient debugging and programming of devices.

Uploaded by

SAI SIVASANKAR
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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NEOCRUX SYSTEMS NEOCRUX SYSTEMS

Understanding JTAG Interface in


Embedded Systems
What is JTAG?

 JTAG = Joint Test Action Group, standardized as IEEE 1149.1

 Interface primarily used for:


oDebugging embedded systems
oIn-system programming (ISP)
oBoundary scan testing 2
Historical Context

 1985: JTAG group formed to simplify PCB testing

 1990: IEEE 1149.1 standard published

 1999: Adopted widely by ARM, MIPS, and DSP processors

 Present: Standard debug method for FPGAs, SoCs, MCUs (e.g. STM32)

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JTAG Pinout (ARM Example)

Signal Description
TDI Test Data In
TDO Test Data Out
TCK Test Clock
TMS Test Mode Select
TRST Optional: Test Reset
GND Common Ground

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JTAG Block Diagram

 TAP (Test Access Port)


 Instruction Register
 Boundary Scan Chain
 Core Debug Module
 Connections to MCU/FPGA pins

5
Applications of JTAG

In-System Programming (flash MCUs, FPGAs)


Debugging (halt/run, breakpoints, register inspection)
Boundary Scan Testing
Check soldering issues
Pin-level access even without firmware
Chain Devices Together: Debug multiple chips via shared TDI/TDO

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JTAG vs SWD (Serial Wire Debug)

Feature JTAG SWD

Pins used 4–5 2

Speed Slower Faster

Debug chains Multi-chip Single

ARM support Yes Yes

Complexity Medium Simple

STM32F4 MCUs support both via SWJ-DP (Serial Wire JTAG Debug Port)

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 JTAG in STM32

ARM Cortex-M Debug Access Port (DAP):


Supports both SWD and JTAG
Use ST-Link, J-Link, OpenOCD,etc…

SWJ-DP Mode: Select between JTAG/SWD via CubeMX or reset sequence


8
 JTAG in STM32 : implementation

PCB layout 3D View

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Tools & Connectors

Software Hardware:
STM32CubeIDE, OpenOCD, Keil µVision, GDB ST-Link V2, SEGGER J-Link, Olimex ARM-USB-TINY

Connector Standards
20-pin ARM JTAG
10-pin Cortex Debug
Tag-Connect (no header)

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Advanced JTAG Uses

ETM Trace Port (External trace with TPIU)

Flash breakpoints without RAM usage

Power debugging (current profiling via tools)

Secure JTAG: Fuse lock, authentication-based access

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