AT90USB64/128
Table 9-2.
Reset and Interrupt Vectors Placement(1)
BOOTRST
IVSEL
Reset Address
0x0000
Interrupt Vectors Start Address
1
1
0
0
0
1
0
1
0x0002
0x0000
Boot Reset Address + 0x0002
0x0002
Boot Reset Address
Boot Reset Address
Boot Reset Address + 0x0002
Note:
1. The Boot Reset Address is shown in Table 28-8 on page 366. For the BOOTRST Fuse “1”
means unprogrammed while “0” means programmed.
9.1.1
9.1.2
Moving Interrupts Between Application and Boot Space
The General Interrupt Control Register controls the placement of the Interrupt Vector table.
MCU Control Register – MCUCR
Bit
7
6
–
R
0
5
–
R
0
4
3
–
R
0
2
–
R
0
1
0
JTD
R/W
0
PUD
R/W
0
IVSEL
R/W
0
IVCE
R/W
0
MCUCR
Read/Write
Initial Value
• 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 beginning of the Boot
Loader section of the Flash. The actual address of the start of the Boot Flash Section is deter-
mined by the BOOTSZ Fuses. Refer to the section “Memory Programming” on page 368 for
details. To avoid unintentional changes of Interrupt Vector tables, a special write procedure must
be followed to change the IVSEL bit:
a. Write the Interrupt Vector Change Enable (IVCE) bit to one.
b. Within four cycles, write the desired value to IVSEL while writing a zero to IVCE.
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 following 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:
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 programed, interrupts are dis-
abled while executing from the Boot Loader section. Refer to the section “Memory Programming”
on page 368 for details on Boot Lock bits.
• Bit 0 – IVCE: Interrupt Vector Change Enable
71
7593A–AVR–02/06
ATMEL [ ATMEL ]
