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NOTE: As of v5.9 the JTAG terminal library was moved to the Bus Pirate bonus/extras firmware.

Bus Pirate firmware v5+ (main firmware) includes support for the OpenOCD JTAG debugger instead, this is a much better option.



  • Bus: JTAG (Joint Test Action Group).
  • Connections: 4 connections (TDI, TCK, TDO, TMS) and ground.
  • Output type: 3.3volt normal, or open collector (pull-up resistors required).
  • Pull-up resistors: required for open collector output mode (2K – 10K).
  • Maximum voltage: 5.5volts (5volt safe).
  • Last documentation update: v5.6.

JTAG is actually a protocol over SPI. This library performs common JTAG functions and manages the JTAG state machine. Read more about JTAG mode here.

Configuration options

Output type - open drain/open collector (high=Hi-Z, low=ground) , normal (high=3.3volts, low=ground). Use open drain/open collector output types with pull-up resistors for multi-voltage interfacing.


A/a/@ Toggle auxiliary pin. Capital “A” sets AUX high, small “a” sets to ground. @ sets aux to input (high impedance mode) and reads the pin value.
D/d Measure voltage on the ADC pin (v1+ hardware only).
W/w Capital ‘W’ enables the on-board power supplies. Small ‘w’ disables them. (v1+ hardware only).
[ Move JTAG state machine (SM) to INSTRUCTION register. Last bit of byte writes is delayed until leaving the INSTRUCTION register.
{ Move JTAG SM to DATA register.
] or } Move JTAG SM to IDLE register.
r Read one byte. (r:1…255 for bulk reads)
0b Write this binary value. Format is 0b00000000 for a byte, but partial bytes are also fine: 0b1001.
0x Write this HEX value. Format is 0×01. Partial bytes are fine: 0xA. A-F can be lower-case or capital letters.
0-255 Write this decimal value. Any number not preceded by 0x or 0b is interpreted as a decimal value.
, Value delimiter. Use a coma or space to separate numbers. Any combination is fine, no delimiter is required between non-number values: {0xa6,0, 0 16 5 0b111 0haF}.
& Delay 1uS. (&:1…255 for multiple delays)
(#) Run macro, (0) for macro list
^ Send one clock tick. (^:1…255 for multiple clock ticks)
/ or \ Toggle clock level high (/) and low (\). Includes clock delay (100uS).
- or _ Toggle data state high (-) and low (_). Includes data setup delay (20uS).
 ! Read one bit with clock.
. Read data pin state (no clock).


0 Macro menu
1 Reset chain
2 Probe chain
3 XSVF player. JTAG programmer. (deprecated)