Datasheet

55
ATmega48/88/168 Automotive [DATASHEET]
7530K–AVR–07/14
When the BOOTRST fuse is programmed and the boot section size set to 2Kbytes, the most typical and general program
setup for the reset and interrupt vector addresses in Atmel
®
ATmega168 is:
Address Labels Code Comments
.org 0x0002
0x0002 jmp EXT_INT0 ; IRQ0 Handler
0x0004 jmp EXT_INT1 ; IRQ1 Handler
... ... ... ;
0x0032 jmp SPM_RDY ; Store Program Memory Ready Handler
;
.org 0x1C00
0x1C00 RESET: ldi r16,high(RAMEND); Main program start
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 determined by the BOOTSZ fuses. Refer to the Section 24. “Boot Loader Support – Read-While-
Write Self-Programming, ATmega88 and ATmega168” on page 229 for details. To avoid unintentional changes of interrupt
vector tables, a special write procedure must be followed to change the IVSEL bit:
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.
Bit 76543210
– – – PUD – – IVSEL IVCE MCUCR
Read/Write R R R R/W R R R/W R/W
Initial Value00000000