
244
7799D–AVR–11/10
ATmega8U2/16U2/32U2
24. debugWIRE On-chip Debug System
24.1
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
24.2
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.
24.3
Physical Interface
When the debugWIRE Enable (DWEN) Fuse is programmed and Lock bits are unprogrammed,
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 and becomes the communication gateway
between target and emulator.
Figure 24-1.
The debugWIRE Setup
Figure 24-1 shows the schematic of a target MCU, with debugWIRE enabled, and the emulator
 connector. The system clock is not affected by debugWIRE and will always be the clock source
selected by the CKSEL Fuses.
dW
GND
dW(RESET)
VCC
2.7 - 5.5
(S
ee
N
ot
e)