JTAG Daisy-Chaining

The JTAG interface allows for several devices to be connected to a single interface in a daisy-chain configuration. The target devices must all be powered by the same supply voltage, share a common ground node, and must be connected as shown in the figure below.

Figure 1. JTAG Daisy-Chain

When connecting devices in a daisy-chain, the following points must be considered:


Daisy-chaining example: TDI → ATmega1280 → ATxmega128A1 → ATUC3A0512 → TDO.

To connect to the Microchip AVR XMEGA device, the daisy-chain settings are:

Table 1. IR Lengths of Microchip MCUs
Device Type IR Length
AVR 8-bit 4 bits
AVR 32-bit 5 bits
SAM 4 bits