JTAG (Joint Test Action Group)
Definition
The industry group that produced IEEE standard 1149.1, which defines the test access port and boundary-scan architecture built into most modern integrated circuits. In forensics, 'JTAG' refers to the technique of using this port to read device memory directly.
- Standard
- IEEE 1149.1
- Function
- Test access port and boundary-scan architecture
- Forensic use
- Direct chip memory read via the test port
- Common target
- Mobile and embedded devices
Common questions
How does JTAG acquisition differ from chip-off?+
JTAG reads memory through the device's existing test access port without removing any component, while chip-off physically desolders the memory chip and reads it in a dedicated chip reader.
When would an examiner choose JTAG over a logical extraction?+
Typically when the device is locked, damaged, or does not support standard logical or physical extraction, and a documented JTAG access point exists for that specific device model.
Related terms
- Chip-Off Acquisition
- A physical extraction method in which the flash memory chip is desoldered from the device's circuit board and read directly with specialised...
- eMMC (Embedded MultiMediaCard)
- A flash storage standard that packages NAND memory chips and a controller into one soldered module using a parallel interface. Common in...
- ISP (In-System Programming)
- A variant of direct chip access that connects to the eMMC command and data pins while the chip is still on the...
- Pinout
- A diagram or database entry that maps each physical contact on a device's circuit board to its signal function. For JTAG acquisition,...
- Test Access Port (TAP)
- The set of four or five contact pads (TDI, TDO, TCK, TMS, and optionally TRST) on a circuit board that implement the...