Datasheet

314

ATmega640/1280/1281/2560/2561

2549K–AVR–01/07

Boundary-scan Related

MCUCR – MCU Control

The MCU Control Register contains control bits for general MCU functions.

• Bits 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. Note that this bit must not be altered when using the On-chip

Debug system.

MCUSR – MCU Status

The MCU Status Register provides information on which reset source caused an MCU

reset.

• 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 Power-on Reset, or

by writing a logic zero to the flag.

Bit 76543210

0x35 (0x55) JTD

– – PUD – – IVSEL IVCE MCUCR

Read/Write R/W RRR/W RRR/W R/W

Initial Value 0 0 0 0 0 0 0 0

Bit 76543210

0x34 (0x54)

– – –JTRFWDRF BORF EXTRF PORF MCUSR

Read/Write R R R R/W R/W R/W R/W R/W

Initial Value 0 0 0 See Bit Description