ATtiny13A datasheet(97/174 Pages) ATMEL

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8126D–AVR–11/09

ATtiny13A

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

• Pull-Up resistor on the dW/(RESET) line must be in the range of 10k to 20 k

Ω. However, the

pull-up resistor is optional.

• Connecting the RESET pin directly to VCC will not work.

• Capacitors inserted on the RESET pin must be disconnected when using debugWire.

• All external reset sources must be disconnected.

15.4 Software Break Points

debugWIRE supports Program memory Break Points by the AVR Break instruction. Setting a

Break Point in AVR Studio® will insert a BREAK instruction in the Program memory. The instruc-

tion 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 a Break Point is changed. This is automatically

handled by 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.

15.5 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 (AVR Studio). See the debugWIRE docu-

mentation for detailed description of the limitations.

The debugWIRE interface is asynchronous, which means that the debugger needs to synchro-

nize to the system clock. If the system clock is changed by software (e.g. by writing CLKPS bits)

communication via debugWIRE may fail. Also, clock frequencies below 100 kHz may cause

communication problems.

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.

15.6 Register Description

The following section describes the registers used with the debugWire.

15.6.1

DWDR –debugWire Data Register

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

765

4321

0x2E

DWDR[7:0]

DWDR

Read/Write

R/W

Initial Value

000

0000

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