ATMEGA644PV ATMEL [ATMEL Corporation], ATMEGA644PV Datasheet - Page 273

• Manufacturer Part Number: ATMEGA644PV
• Description: 8-bit Microcontroller with 16/32/64K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

23.8
23.8.1
23.8.2
8011D–AVR–02/07
Register Description
MCUCR – MCU Control Register
MCUSR – MCU Status Register
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.
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
0x35 (0x55)
Read/Write
Initial Value
Bit
0x34 (0x54)
Read/Write
Initial Value
JTD
R/W
7
0
R
7
–
0
BODS
R
6
0
R
6
–
0
BODSE
R
5
0
R
5
–
0
JTRF
PUD
R/W
R/W
4
0
4
ATmega164P/324P/644P
WDRF
R/W
R
3
–
0
3
See Bit Description
BORF
R/W
R
2
–
0
2
EXTRF
IVSEL
R/W
R/W
1
0
1
PORF
IVCE
R/W
R/W
0
0
0
MCUCR
MCUSR
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