ATMEGA2561V ATMEL [ATMEL Corporation], ATMEGA2561V Datasheet - Page 76

• Manufacturer Part Number: ATMEGA2561V
• Description: 8-bit Microcontroller with 64K/128K/256K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Register Description
MCUCR – MCU Control
Register
76
ATmega640/1280/1281/2560/2561
• Bit 1 – IVSEL: Interrupt Vector Select
When the IVSEL bit is cleared (zero), the Interrupt Vectors are placed at the start of the
Flash memory. When this bit is set (one), the Interrupt Vectors are moved to the begin-
ning of the Boot Loader section of the Flash. The actual address of the start of the Boot
Flash Section is determined by the BOOTSZ Fuses. Refer to the section “Memory Pro-
gramming” on page 342 for details. To avoid unintentional changes of Interrupt Vector
tables, a special write procedure must be followed to change the IVSEL bit (see “Moving
Interrupts Between Application and Boot Section” on page 74):
Interrupts will automatically be disabled while this sequence is executed. Interrupts are
disabled in the cycle IVCE is set, and they remain disabled until after the instruction fol-
lowing the write to IVSEL. If IVSEL is not written, interrupts remain disabled for four
cycles. The I-bit in the Status Register is unaffected by the automatic disabling.
Note:
• Bit 0 – IVCE: Interrupt Vector Change Enable
The IVCE bit must be written to logic one to enable change of the IVSEL bit. IVCE is
cleared by hardware four cycles after it is written or when IVSEL is written. Setting the
IVCE bit will disable interrupts, as explained in the IVSEL description.
Bit
0x35 (0x55)
Read/Write
Initial Value
1. Write the Interrupt Vector Change Enable (IVCE) bit to one.
2. Within four cycles, write the desired value to IVSEL while writing a zero to
IVCE.
If Interrupt Vectors are placed in the Boot Loader section and Boot Lock bit BLB02 is pro-
grammed, interrupts are disabled while executing from the Application section. If
Interrupt Vectors are placed in the Application section and Boot Lock bit BLB12 is pro-
gramed, interrupts are disabled while executing from the Boot Loader section. Refer to
the section “Memory Programming” on page 342 for details on Boot Lock bits.
JTD
R/W
7
0
R
6
–
0
R
5
–
0
PUD
R/W
4
0
R
3
–
0
R
2
–
0
IVSEL
R/W
1
0
IVCE
R/W
0
0
2549K–AVR–01/07
MCUCR