MC68HC908GZ8 Datasheet, PDF (264/344 Pages) Motorola, Inc – Microcontrollers

System Integration Module (SIM)
Interrupts are latched, and arbitration is performed in the SIM at the start of
interrupt processing. The arbitration result is a constant that the CPU uses to
determine which vector to fetch. Once an interrupt is latched by the SIM, no other
interrupt can take precedence, regardless of priority, until the latched interrupt is
serviced (or the I bit is cleared). See Figure 20-10.
FROM RESET
I BBIRTESAEKT?
INTERRUPT?
NO
YES
I BIT SET?
NO
IRQ
INTERRUPT?
NO
AS MANY INTERRUPTS
AS EXIST ON CHIP
YES
YES
STACK CPU REGISTERS
SET I BIT
LOAD PC WITH INTERRUPT VECTOR
FETCH NEXT
INSTRUCTION
SWI
INSTRUCTION?
YES
NO
RTI
YES
INSTRUCTION?
NO
UNSTACK CPU REGISTERS
EXECUTE INSTRUCTION
Figure 20-10. Interrupt Processing
Data Sheet
264
System Integration Module (SIM)
MC68HC908GZ8
Freescale Semiconductor