JTAG for ARM
Overview
The JTAG Interface of certain embedded processors can be used to debug the firmware running and to program new software. Most Jtag Interfaces are compatible to IEEE1149.1, but there are differences in the exact pin-out and supported voltages. Using an ICnova equipped with an ARM-processor, JTAG-adaptors with 10 or 20 pins are common. Usually the JTAG-Interface is in use only, if the bootloader of a specific board must be modified or was overwritten accidentally.
10-pin JTAG-Adaptor
Certain programmers, eg the ICprog OpenOCD, can be used directly to interface the board by a straight 10-pin cable. This programmer is compatible to the OpenOCD project. Using other programmers, the exact pinout of the interface has to be checked.
20-pin JTAG-Adaptor
There are a lot of other programmers, which can be used to program the ARM-based ICnova modules. Most of them have a 20-pin interface. Before choosing one, it should be made sure, that the programmer can be accessed by the correct Software on the PC, eg. OpenOCD. The 20-pin connector can be adapted using the following pinning scheme:
| Signal | 20 pin | 10 pin |
|---|---|---|
| Vref | 1 | 4 |
| Vsupply | 2 | 7 |
| TRST | 3 | 8 |
| GND | 4 | 2,10 |
| TDI | 5 | 9 |
| GND | 6 | 2,10 |
| TMS | 7 | 5 |
| GND | 8 | 2,10 |
| TCK | 9 | 1 |
| GND | 10 | 2,10 |
| RTCK | 11 | NC |
| GND | 12 | 2,10 |
| TDO | 13 | 3 |
| GND | 14 | 2,10 |
| nRST | 15 | 6 |
| GND | 16 | 2,10 |
| NC | 17 | NC |
| GND | 18 | 2,10 |
| NC | 19 | NC |
| GND | 20 | 2,10 |