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JTAG (Joint Test Action Group)

JTAG (Joint Test Action Group) is an international test protocol (IEEE 1149.1) for on-chip testing; many advanced devices (DSP, FPGA, etc.) support it. Interfaces: TCK, TMS, TDI, TDO, and TRST (TDO is output). A TAP (Test Access Port) is defined inside the device and exercised with a JTAG tool.

With cJTAG enabled, TDI/TDO are field disabled (Disable); TCK/TMS act as TCKC/TMSC in OScan1. Instruction decode may decide whether TRST is required. See Settings.

Decode Settings

Decode Settings

JTAG Decode Settings
  • Channel: Assign TCK / TMS / TDI / TDO / TRST. TRST is optional; field enabled (Enable) when checkedchecked.
  • cJTAG: Disables TDI/TDO fields; TCK/TMS as TCKC/TMSC. Default: cleared.

JTAG Advanced

Advanced settings
  • Show test data: In Shift-IR / Shift-DR, show TDI or TDO in hex. Default: show TDO.
    • Test data bit order: LSB First / MSB First. Default: index 0 (LSB First).
    • Interpreter Instruction: Enable the instruction list; show IR contents at Update-IR. Edit JtagInst.txt, then Refresh. Default: checked.
    • Acute Jtag Instruction table (JtagInst.txt): Provided by the Jtag DLL; editable; BSDL can be added. See appendix.

JTAG Report

Report display
  • Show TDI or/and TDO: “Show TDI and TDO” shows both. Default: Show 1 data.
  • TAP state display: Default: all states checked.

Result

JTAG Result

JTAG decode result

Appendix: Acute JTAG Instruction table (JtagInst.txt)

Numbers are hexadecimal.

  • ##: comment
  • #ID: list ID 00–FF; must be sequential
  • #NAME: set name (max 32 bytes)
  • #LENGTH: instruction length in bits
  • #CAPTURE: Capture-IR value
  • #INST: code, name; empty #INST: ends the list
  • #TRST: 1 if TRST needed; 0 or omit if not
  • #BSDL: full BSDL path

Example: same as the traditional sample (#ID:00 … #BSDL:C:\3256at144_1532.bsd).