Basic init code
lea $10F300, sp lea $10F300, a7 ; Depends on assemblers move.b d0,REG_DIPSW ; Kick watchdog move.w #7,REG_IRQACK ; Acknowledge any pending interrupts move.w #$2700,sr ; Disable all interrupts
Clearing the 68k user RAM:
lea RAMSTART,a0 move.l #($F300/4)-1,d0 ; User RAM's size is $F300, and we clear longwords (4 bytes) clram: clr.l (a0)+ dbra d0,clram
Note that this function also clears the stack. Don't make a subroutine out of it unless you're sure that the return address won't be cleared.
Don't forget to kick the watchdog regularly in your init code if the VBL interrupt isn't enabled or doesn't kick it itself.