ATmega64A datasheet(280/392 Pages) ATMEL

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280

8160C–AVR–07/09

ATmega64A

25.7

Boundary-scan Description Language Files

Boundary-scan Description Language (BSDL) files describe Boundary-scan capable devices in

a standard format used by automated test-generation software. The order and function of bits in

the Boundary-scan Data Register are included in this description.

25.8

Boundary-scan Related Register in I/O Memory

25.8.1

MCUCSR – MCU Control and Status Register

The MCU Control and Status Register contains control bits for general MCU functions, and pro-

vides information on which reset source caused an MCU Reset.

• Bit 7 – JTD: JTAG Interface Disable

When this bit is zero, the JTAG interface is enabled if the JTAGEN Fuse is programmed. If this

bit is one, the JTAG interface is disabled. In order to avoid unintentional disabling or enabling of

the JTAG interface, a timed sequence must be followed when changing this bit: The application

software must write this bit to the desired value twice within four cycles to change its value.

If the JTAG interface is left unconnected to other JTAG circuitry, the JTD bit should be set to

one. The reason for this is to avoid static current at the TDO pin in the JTAG interface.

• Bit 4 – JTRF: JTAG Reset Flag

This bit is set if a reset is being caused by a logic one in the JTAG Reset Register selected by

the JTAG instruction AVR_RESET. This bit is reset by a Brown-out Reset, or by writing a logic

zero to the flag.

Bit

5432

0x34 (0x54)

JTD

–

–JTRF

WDRF

BORF

EXTRF

PORF

MCUCSR

Read/Write

R/W

Initial Value

See Bit Description

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