ATmega32A datasheet(227/352 Pages) ATMEL

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227

8155B–AVR–07/09

ATmega32A

23. JTAG Interface and On-chip Debug System

23.1

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 Breakpoints on Single Address or Address Range

– Data Memory Breakpoints 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®

23.2

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 “Program-

ming via the JTAG Interface” on page 284 and “IEEE 1149.1 (JTAG) Boundary-scan” on page

233, respectively. The On-chip Debug support is considered being private JTAG instructions,

and distributed within ATMEL and to selected third party vendors only.

Figure 23-1 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 testing. The JTAG Programming Interface (actually consisting of several physical

and virtual Data Registers) is used for JTAG Serial Programming via the JTAG interface. The

Internal Scan Chain and Break Point Scan Chain are used for On-chip Debugging only.

23.3

TAP – Test Access Port

The JTAG interface is accessed through four of the AVR’s pins. In JTAG terminology, these pins

constitute the Test Access Port – TAP. These pins are:

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