Datasheet

System Integration Module (SIM)
Technical Data MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3
106 System Integration Module (SIM) Freescale Semiconductor
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.
At the beginning of an interrupt, the CPU saves the CPU register
contents on the stack and sets the interrupt mask (I bit) to prevent
additional interrupts. At the end of an interrupt, the RTI instruction
recovers the CPU register contents from the stack so that normal
processing can resume. Figure 8-9 shows interrupt entry timing. Figure
8-10 shows interrupt recovery timing.
Figure 8-9. Interrupt Entry
Figure 8-10. Interrupt Recovery
MODULE
IDB
R/W
INTERRUPT
DUMMY
SP SP – 1 SP – 2 SP – 3 SP – 4 VECT H VECT L START ADDR
IAB
DUMMY PC – 1[7:0] PC – 1[15:8] X A CCR V DATA H V DATA L OPCODE
I BIT
MODULE
IDB
R/W
INTERRUPT
SP – 4 SP – 3 SP – 2 SP – 1 SP PC PC + 1
IAB
CCR A X PC –1 [15:8] PC – 1[7:0] OPCODE OPERAND
I BIT