Programming header

The XMEGA can be programmed and debugged by connecting an external programming/debugging tool to the “JTAG & PDI” header. The header has a standard pin-out and therefore tools like the JTAGICE3 or AVR ONE! can be connected to the header.

Note:

Pin 1 on the JTAG header is at the top right corner and is marked with a square pad.

Table 1. JTAG and PDI interface header on the XMEGA-A3BU Xplained
Pin on header	JTAG	PDI
1	TCK	-
2	GND¹	GND¹
3	TDO	DATA
4	VCC	VCC
5	TMS	-
6	nSRST	CLK
7	-	-
8	-	-
9	TDI	-
10	GND¹	GND¹

Because JTAG TDO and PDI DATA are connected on the PCB for this kit, JTAG must be disabled on the device in order to use PDI. The reason for this is that when JTAG is enabled it will enable a pull-up internally on TDO which interferes with the PDI initialization sequence.

This will also be an issue when the application on the device uses the JTAG_TDO pin. Nevertheless it is possible to use the pin if the TDO signal is disconnected from the PDI DATA signal by cutting a strap on the back side of the PCB (the cut strap J203 is on the back side of the board and marked with a text that describes its function). This however will disable the JTAG interface until the connection is re-established by e.g. soldering a bridge on the cut-strap.