Rainbow-electronics ATmega8HVD Manual de usuario descargar pdf (Pagina 119)

119

8052B–AVR–09/08

ATmega4HVD/8HVD

22. debugWIRE On-chip Debug System

22.1 Features

• Complete Program Flow Control

• Emulates All On-chip Functions, both Digital and Analog, except RESET Pin

• Real-time Operation

• Symbolic Debugging Support (Both at C and Assembler Source Level, or for Other HLLs)

• Unlimited Number of Program Break Points (Using Software Break Points)

• Non-intrusive Operation

• Electrical Characteristics Identical to Real Device

• Automatic Configuration System

• High-Speed Operation

• Programming of Non-volatile Memories

22.2 Overview

The debugWIRE On-chip debug system uses a One-wire, bi-directional interface to control the

program flow, execute AVR instructions in the CPU and to program the different non-volatile

memories.

22.3 Physical Interface

When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unpro-

grammed, the debugWIRE system within the target device is activated. The RESET port pin is

configured as a wire-AND (open-drain) bi-directional I/O pin with pull-up enabled and becomes

the communication gateway between target and emulator.

Figure 22-1. The debugWIRE Setup

Figure 22-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emula-

tor connector. The system clock is not affected by debugWIRE and will always be the clock

source selected by the CKSEL Fuses.

When designing a system where debugWIRE will be used, the following observations must be

made for correct operation:

• Pull-up resistors on the dW/(RESET

) line must not be smaller than 10kΩ. The pull-up

resistor is not required for debugWIRE functionality.

• Connecting the RESET

pin directly to V

will not work.

GND

dW(RESET)

VFET

2.1 - 6.0

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Rainbow-electronics ATmega8HVD Manual de usuario Pagina 119