Datasheet

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 10 kΩ. The pull-up resistor is

not required for debugWIRE functionality.

• Connecting the RESET pin directly to V

will not work.

• Capacitors connected to the RESET pin must be disconnected when using debugWire.

• All external reset sources must be disconnected.

29.4 Software Breakpoints

debugWIRE supports the breakpoint functions in program memory by the AVR BREAK instruction.

Setting a breakpoint in Atmel Studio will insert a BREAK instruction in the program memory. The

instruction replaced by the BREAK instruction will be stored. When program execution is continued, the

stored instruction will be executed before continuing from the program memory. A break can be inserted

manually by putting the BREAK instruction in the program.

The Flash must be re-programmed each time when a breakpoint is changed. This is automatically

handled by Atmel Studio through the debugWIRE interface. The use of breakpoints will, therefore, reduce

the Flash data retention. Devices used for debugging purposes should not be shipped to end customers.

29.5 Limitations of debugWIRE

The debugWIRE communication pin (dW) is physically located on the same pin as external Reset

(RESET). An external Reset source is therefore not supported when the debugWIRE is enabled.

A programmed DWEN fuse enables some parts of the clock system to be running in all sleep modes. This

will increase the power consumption while in sleep. Thus, the DWEN fuse should be disabled when

debugWire is not used.

29.6 Register Description

The following section describes the registers used with the debugWire.

ATmega48PA/88PA/168PA

debugWIRE On-chip Debug System

Datasheet Complete

DS40002011A-page 335