Atmel AVR - Debugging Interfaces - JTAG

JTAG

JTAG provides access to on-chip debugging functionality while the chip is running in the target system. JTAG allows accessing internal memory and registers, setting breakpoints on code, and single-stepping execution to observe system behaviour.

Atmel provides a series of JTAG adapters for the AVR:

1. The JTAGICE 3 is the latest member of the JTAGICE family (JTAGICE mkIII). It supports JTAG, aWire, SPI, and PDI interfaces.
2. The JTAGICE mkII replaces the JTAGICE, and is similarly priced. The JTAGICE mkII interfaces to the PC via USB, and supports both JTAG and the newer debugWIRE interface. Numerous 3rd-party clones of the Atmel JTAGICE mkII device started shipping after Atmel released the communication protocol.

1. The AVR Dragon is a low-cost (approximately $50) substitute for the JTAGICE mkII for certain target parts. The AVR Dragon provides in-system serial programming, high-voltage serial programming and parallel programming, as well as JTAG or debugWIRE emulation for parts with 32 KB of program memory or less. ATMEL changed the debugging feature of AVR Dragon with the latest firmware of AVR Studio 4 - AVR Studio 5 and now it supports devices over 32 KB of program memory.
2. The JTAGICE adapter interfaces to the PC via a standard serial port. The JTAGICE has been End-Of-Lifed, though it is still supported in AVR Studio and other tools.

JTAG can also be used to perform a Boundary Scan test, which tests the electrical connections between AVRs and other Boundary Scan capable chips in a system. Boundary scan is well-suited for a production line; the hobbyist is probably better off testing with a multimeter or oscilloscope.