PCIF0 datasheet(227/294 Pages) ATMEL

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227

9219A–RFID–01/11

Atmel ATA5505 [Preliminary]

• Pull-up resistors on the dW/(RESET) line must not be smaller than 10k

Ω. The pull-up

resistor is not required for debugWIRE functionality.

• Connecting the RESET pin directly to V

CC will not work.

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

• All external reset sources must be disconnected.

20.4

Software Break Points

DebugWIRE supports Program memory break points by the Atmel

® AVR® BREAK instruction.

Setting a break point in Atmel AVR 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 Pro-

gram memory. A break can be inserted manually by putting the BREAK instruction in the

program.

The Flash must be re-programmed each time a break point is changed. This is automatically

handled by Atmel AVR Studio through the debugWIRE interface. The use of break points will

therefore reduce the Flash Data retention. Devices used for debugging purposes should not

be shipped to end customers.

20.5

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.

The debugWIRE system accurately emulates all I/O functions when running at full speed, i.e.,

when the program in the CPU is running. When the CPU is stopped, care must be taken while

accessing some of the I/O Registers via the debugger (Atmel AVR Studio).

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.

20.6

DebugWIRE Related Register in I/O Memory

The following section describes the registers used with the debugWire.

20.6.1

DebugWIRE Data Register – DWDR

The DWDR Register provides a communication channel from the running program in the MCU

to the debugger. This register is only accessible by the debugWIRE and can therefore not be

used as a general purpose register in the normal operations.

Bit

543210

DWDR[7:0]

DWDR

Read/Write

R/W

Initial Value

000000

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