ATmega325P datasheet(227/364 Pages) ATMEL

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227

8023F–AVR–07/09

ATmega325P/3250P

A debugger, like the AVR Studio, may however use one or more of these resources for its inter-

nal purpose, leaving less flexibility to the end-user.

A list of the On-chip Debug specific JTAG instructions is given in ”On-chip Debug Specific JTAG

Instructions” on page 227.

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 either of the LB1 or

LB2 Lock bits are set. Otherwise, the On-chip debug system would have provided 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 Cor-

poration’s AVR Assembler and C programs compiled with third party vendors’ compilers.

AVR Studio runs under Microsoft

® Windows® 95/98/2000, Windows NT® and Windows XP®.

For a full description of the AVR Studio, please refer to the AVR Studio User Guide. Only high-

lights 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 execution, 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.

22.7

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.

22.7.1

PRIVATE0; 0x8

Private JTAG instruction for accessing On-chip debug system.

22.7.2

PRIVATE1; 0x9

Private JTAG instruction for accessing On-chip debug system.

22.7.3

PRIVATE2; 0xA

Private JTAG instruction for accessing On-chip debug system.

22.7.4

PRIVATE3; 0xB

Private JTAG instruction for accessing On-chip debug system.

22.8

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 program-

ming (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 MCUCR Register must be cleared to enable the

JTAG Test Access Port.

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