68
8025I–AVR–02/09
ATmega48P/88P/168P/328P
.org 0x3C00
0x3C00
RESET: ldi
r16,high(RAMEND); Main program start
0x3C01
out
SPH,r16
; Set Stack Pointer to top of RAM
0x3C02
ldi
r16,low(RAMEND)
0x3C03
out
SPL,r16
0x3C04
sei
; Enable interrupts
0x3C05
<instr> xxx
When the BOOTRST Fuse is programmed, the Boot section size set to 2K bytes and the IVSEL
bit in the MCUCR Register is set before any interrupts are enabled, the most typical and general
program setup for the Reset and Interrupt Vector Addresses in ATmega328P is:
Address
Labels Code
Comments
;
.org 0x3C00
0x3C00
jmp
RESET
; Reset handler
0x3C02
jmp
EXT_INT0
; IRQ0 Handler
0x3C04
jmp
EXT_INT1
; IRQ1 Handler
...
...
...
;
0x3C32
jmp
SPM_RDY
; Store Program Memory Ready Handler
;
0x3C33
RESET: ldi
r16,high(RAMEND); Main program start
0x3C34
out
SPH,r16
; Set Stack Pointer to top of RAM
0x3C35
ldi
r16,low(RAMEND)
0x3C36
out
SPL,r16
0x3C37
sei
; Enable interrupts
0x3C38
<instr> xxx
9.5
Register Description
9.5.1
Moving Interrupts Between Application and Boot Space, ATmega88P, ATmega168P and ATmega328P
The MCU Control Register controls the placement of the Interrupt Vector table.
9.5.2
MCUCR – MCU Control Register
• 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
”Boot Loader Support – Read-While-Write
Self-Programming, ATmega88P, ATmega168P and ATmega328P” on page 277
avoid unintentional changes of Interrupt Vector tables, a special write procedure must be fol-
lowed to change the IVSEL bit:
Bit
7
6
5
4
3
2
1
0
–
BODS
BODSE
PUD
–
–
IVSEL
IVCE
MCUCR
Read/Write
R
R
R
R/W
R
R
R/W
R/W
Initial Value
0
0
0
0
0
0
0
0