Datasheet

60
8018P–AVR–08/10
ATmega169P
11.2.1 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” on page 280 for details.
• 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 description in ”Moving Interrupts Between Application and Boot
Space” on page 59. See Code Example.
Assembly Code Example
Move_interrupts:
; Get MCUCR
in r16, MCUCR
mov r17, r16
; Enable change of Interrupt Vectors
ori r16, (1<<IVCE)
out MCUCR, r16
; Move interrupts to Boot Flash section
ori r17, (1<<IVSEL)
out MCUCR, r17
ret
C Code Example
void Move_interrupts(void)
{
uchar temp;
/* Get MCUCR*/
temp = MCUCR;
/* Enable change of Interrupt Vectors */
MCUCR = temp | (1<<IVCE);
/* Move interrupts to Boot Flash section
*/ MCUCR = temp | (1<<IVSEL);
}
Bit 76543210
0x35 (0x55)
JTD - - PUD – – IVSEL IVCE MCUCR
Read/Write R/W R R R/W R R R/W R/W
Initial Value00000000