All Common JTAG Pinout
Official ARM 20-pin Header / JTAG connector pin-out
VTref 1 2 Vsupply
nTRST 3 4 GND
TDI 5 6 GND
TMS 7 8 GND
TCK 9 10 GND
RTCK 11 12 GND
TDO 13 14 GND
nSRST 15 16 GND
DBGRQ 17 18 GND
DBGACK 19 20 GND
Guide Lines for building your Target Board JTAG interface
- All ground pins must be connected.
- DBGRQ and DBGACK are rarely used; they connect to lines on the ARM core that are rarely brought out to physical pins and are manipulated via other means (as bits in the jtag chain?).
- nSRST is the system reset (active low) and it is optional but recommended as Multi-ICE and RealView ICE uses is for debug of XScale processors, reset on startup, reset from the debugger, and reset detection and is needed for Auto Configuration on some processors.
- nTRST is optional, it resets the JTAG TAP controller state mahine and the embedded ICE logic. Resetting of the TAP controller can be accomplished by 5 TCK cycles with TMS high> AT91SAM7 CPUs don't bring nTRST to a pin. OpenOCD can be configured to work with or without nTRST and nSRST. Both reset signals are open drain.
- RTCK is an optional readback on the TCK pin and is used for adaptive clocking.
- Vsupply is used to power the JTAG dongle and
- VTref is used to set the thresholds. ARM's official jtag interfaces put a 10K pulldown resistor on these lines.
- ARM recommends 10K pullups/pulldowns with pullups on TMS, TDI, TDO, nSRST, and nTRST and a pulldown (odd) on TCK. Atmel's AT91SAM7 eval board uses pullup on TCK. Multi-ICE, RealView ICE, and OpenOCD support other devices on the JTAG chain, however manual configuration may be required. Multi-ICE uses analog switches (between ground and VTref) to drive the JTAG signals with 100 ohm series resistors.
Minimized ARM 20-pin Header / JTAG connector pin-out
Amontec “JTAGkey 20-pin Header” ( see www.amontec.com/jtagkey.shtml )
VREF 1 2 n.c
TRST_N 3 4 GND
TDI 5 6 GND
TMS 7 8 GND
TCK 9 10 GND
n.c. 11 12 GND
TDO 13 14 GND
SRST_N 15 16 GND
n.c. 17 18 GND
n.c. 19 20 GND
n.c. for not connected
Xilinx JTAG - Altera JTAG - Lattice JTAG pinout
AVR JTAG - MIPS JTAG- XSCALE JTAG - ALL JTAG pinout
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