By creating a JTAG daisy-chain, a single JTAG connector can serve as an ISP interface for several devices. Typical connection for a daisy-chain using JTAG for AVR® Dragon is shown in the following schematic. The daisy-chain configuration can be used for any programmer/debugger that uses JTAG interface. The GND and VTREF of JTAG, which is not shown in the figure, must be connected to the target board.
The protection resistors shown in Figure 1 are required if the JTAG lines are used in the application. For example, ADC input pins often have analog filters on the lines. In such cases, the filter capacitor must be removed while programming, to ensure that the load is resistive. The following figure illustrates the steps.
