Datasheet

Table Of Contents
289
ATmega640/V-1280/V-1281/V-2560/V-2561/V [DATASHEET]
2549Q–AVR–02/2014
27. JTAG Interface and On-chip Debug System
27.1 Features
JTAG (IEEE std. 1149.1 Compliant) Interface
Boundary-scan Capabilities According to the IEEE std. 1149.1 (JTAG) Standard
Debugger Access to:
All Internal Peripheral Units
Internal and External RAM
The Internal Register File
–Program Counter
EEPROM and Flash Memories
Extensive On-chip Debug Support for Break Conditions, Including
AVR Break Instruction
Break on Change of Program Memory Flow
Single Step Break
Program Memory Break Points on Single Address or Address Range
Data Memory Break Points on Single Address or Address Range
Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
On-chip Debugging Supported by AVR Studio
®
27.2 Overview
The AVR IEEE std. 1149.1 compliant JTAG interface can be used for
Testing PCBs by using the JTAG Boundary-scan capability
Programming the non-volatile memories, Fuses and Lock bits
On-chip debugging
A brief description is given in the following sections. Detailed descriptions for Programming via the JTAG interface,
and using the Boundary-scan Chain can be found in the sections “Programming via the JTAG Interface” on page
342 and “IEEE 1149.1 (JTAG) Boundary-scan” on page 295, respectively. The On-chip Debug support is consid-
ered being private JTAG instructions, and distributed within Atmel and to selected third party vendors only.
Figure 27-1 on page 290 shows a block diagram of the JTAG interface and the On-chip Debug system. The TAP
Controller is a state machine controlled by the TCK and TMS signals. The TAP Controller selects either the JTAG
Instruction Register or one of several Data Registers as the scan chain (Shift Register) between the TDI – input
and TDO – output. The Instruction Register holds JTAG instructions controlling the behavior of a Data Register.
The ID-Register, Bypass Register, and the Boundary-scan Chain are the Data Registers used for board-level test-
ing. The JTAG Programming Interface (actually consisting of several physical and virtual Data Registers) is used
for serial programming via the JTAG interface. The Internal Scan Chain and Break Point Scan Chain are used for
On-chip debugging only.