Microchip Technology Power Debugger Manual page 55

4.2.2.2 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 4-3. JTAG Daisy Chain
programmer /
debugger
When connecting devices in a daisy chain, the following points must be considered:
• All devices must share a common ground, connected to GND on the Power Debugger probe
• All devices must be operating on the same target voltage. VTG on the Power Debugger must be connected to
this voltage.
• TMS and TCK are connected in parallel; TDI and TDO are connected in a serial chain.
• nSRST on the Power Debugger probe must be connected to RESET on the devices if any of the devices in the
chain disables its JTAG port
• "Devices before" refers to the number of JTAG devices that the TDI signal has to pass through in the daisy chain
before reaching the target device. Similarly, "devices after" is the number of devices that the signal has to pass
through after the target device before reaching the Power Debugger TDO pin.
• Instruction bits "before" and "after" refers to the total sum of all JTAG devices' instruction register lengths, which
are connected before and after the target device in the daisy chain
• The total IR length (instruction bits before + Microchip target device IR length + instruction bits after) is limited to
a maximum of 256 bits. The number of devices in the chain is limited to 15 before and 15 after.
Tip:
Daisy chaining example: TDI → ATmega1280 → ATxmega128A1 → ATUC3A0512 → TDO.
In order to connect to the Microchip AVR XMEGA device, the daisy chain settings are:
• Devices before: 1
• Devices after: 1
• Instruction bits before: 4 (8-bit AVR devices have 4 IR bits)
• Instruction bits after: 5 (32-bit AVR devices have 5 IR bits)
Table 4-2. IR Lengths of Microchip MCUs
©
2020 Microchip Technology Inc.
TCK
TMS
TDI
TDO
Device Type
AVR 8-bit
AVR 32-bit
SAM
target
target
device
device
2
1
User Guide
Power Debugger
On-chip Debugging
target
device
3
IR Length
4 bits
5 bits
4 bits
DS40002201A-page 55