Datasheet

215
7728G–AVR–06/10
ATtiny87/ATtiny167
19. DebugWIRE On-chip Debug System
19.1 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
19.2 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.
19.3 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 19-1. The debugWIRE Setup
Figure 19-1 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:
Vcc
+1.8 - +5.5V
GND
dW (RESET)dW