
239
ATmega64A [DATASHEET]
8160D–AVR–02/2013
The JTAGEN Fuse must be programmed to enable the JTAG Test Access Port. In addition, the OCDEN Fuse must
be programmed and no Lock bits must be set for the On-chip Debug system to work. As a security feature, the On-
chip Debug system is disabled when any Lock bits are set. Otherwise, the On-chip Debug system would have pro-
vided a back-door into a secured device.
The AVR Studio enables the user to fully control execution of programs on an AVR device with On-chip Debug
capability, AVR In-Circuit Emulator, or the built-in AVR Instruction Set Simulator. AVR Studio supports source level
execution of Assembly programs assembled with Atmel AVR Assembler and C programs compiled with third party
vendors’ compilers.
AVR Studio runs under Microsoft Windows 95/98/2000/XP/NT.
For a full description of the AVR Studio, please refer to the AVR Studio User Guide. Only highlights are presented
in this document.
All necessary execution commands are available in AVR Studio, both on source level and on disassembly level.
The user can execute the program, single step through the code either by tracing into or stepping over functions,
step out of functions, place the cursor on a statement and execute until the statement is reached, stop the execu-
tion, and reset the execution target. In addition, the user can have an unlimited number of code Break Points (using
the BREAK instruction) and up to two data memory Break Points, alternatively combined as a mask (range) Break
Point.
25.7
On-chip Debug Specific JTAG Instructions
The On-chip debug support is considered being private JTAG instructions, and distributed within ATMEL and to
selected third party vendors only. Instruction opcodes are listed for reference.
25.7.1
PRIVATE0; 0x8
Private JTAG instruction for accessing On-chip Debug system.
25.7.2
PRIVATE1; 0x9
Private JTAG instruction for accessing On-chip Debug system.
25.7.3
PRIVATE2; 0xA
Private JTAG instruction for accessing On-chip Debug system.
25.7.4
PRIVATE3; 0xB
Private JTAG instruction for accessing On-chip Debug system.
25.8
Using the JTAG Programming Capabilities
Programming of AVR parts via JTAG is performed via the 4-pin JTAG port, TCK, TMS, TDI, and TDO. These are
the only pins that need to be controlled/observed to perform JTAG programming (in addition to power pins). It is not
required to apply 12V externally. The JTAGEN Fuse must be programmed and the JTD bit in the MCUSR Register
must be cleared to enable the JTAG Test Access Port.
The JTAG programming capability supports:
Flash Programming and verifying
EEPROM Programming and verifying
Fuse Programming and verifying
Lock bit Programming and verifying