2.5.5.4 Chip Access Using JTAG Connection

The JTAG connection is not enabled by default on this chip at delivery due to the secure ROM code implementation.

By default, the device boots in Standard mode and not in Secure mode. When the secure ROM code starts, it disables the JTAG access for the entire boot sequence.

If the secure ROM code does not find any program in the external memory, it enables the USB connection and the serial port and waits for a dedicated command to switch the chip into Secure mode.

If any other character is received, the secure ROM code starts the standard SAM-BA® monitor, locks access to the ROM memory, and enables the JTAG.

The chip can then be accessed using the JTAG connection.

If the secure ROM code finds a bootable program, it automatically disables ROM access and enables the JTAG connection just before launching the program.

The procedure to enable JTAG access is as follows:

• Connect your computer to the board with JTAG and USB (J20 USB-A).
• Power on the chip.
• Open a terminal console (TeraTerm, HyperTerminal, etc.) on your computer and connect to the USB CDC serial COM port.
• Send the '#' character. You will see then the prompt '>' character sent by the device (indicating that the standard SAM-BA Monitor is running).
• Use the Standard SAM-BA Monitor to connect to the chip with JTAG.

Note that it is not necessary to follow this sequence to connect the standard SAM-BA Monitor with USB.