61
7530J–AVR–03/12
Atmel ATmega48/88/168 Automotive
0x1C01
out
SPH,r16
; Set Stack Pointer to top of RAM
0x1C02
ldi
r16,low(RAMEND)
0x1C03
out
SPL,r16
0x1C04
sei
; Enable interrupts
0x1C05
<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 ATmega168 is:
Address Labels Code
Comments
;
.org 0x1C00
0x1C00
jmp
RESET
; Reset handler
0x1C02
jmp
EXT_INT0
; IRQ0 Handler
0x1C04
jmp
EXT_INT1
; IRQ1 Handler
...
;
0x1C32
jmp
SPM_RDY
; Store Program Memory Ready Handler
;
0x1C33
RESET: ldi
r16,high(RAMEND); Main program start
0x1C34
out
SPH,r16
; Set Stack Pointer to top of RAM
0x1C35
ldi
r16,low(RAMEND)
0x1C36
out
SPL,r16
0x1C37
sei
; Enable interrupts
0x1C38
<instr>
xxx
9.3.1
Moving Interrupts Between Application and Boot Space, ATmega88 and ATmega168
The MCU Control Register controls the placement of the Interrupt Vector table.
9.3.2
MCU Control Register – MCUCR
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-
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.
Bit
7
6543
210
–
PUD
–
IVSEL
IVCE
MCUCR
Read/Write
R
R/W
R
R/W
Initial Value
0
0000
000