Fujitsu F2 MC-8FX Family, Hardware Manual

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CHAPTER 8 INTERRUPTS
8.1.5 Stack Operations During Interrupt Processing
This section describes how registers are saved and restored during interrupt
processing.
■
Stack Operation at the Start of Interrupt Processing
Once the CPU accepts an interrupt, it automatically saves the current program counter (PC) and program
status (PS) values onto a stack.
Figure 8.1-5 shows how the stack is used at the start of interrupt processing.
Figure 8.1-5 Stack Operation at Start of Interrupt Processing
■
Stack Operation upon Returning from Interrupt
When the interrupt return instruction (RETI) is executed to end interrupt processing, the program status
(PS) and then the program counter (PC) are restored from the stack, in the reverse order from which they
were saved to the stack when interrupt processing started. This restores the PS and PC values to their states
prior to starting interrupt processing.
Note:
As the accumulator (A) and temporary accumulator (T) are not saved onto the stack automatically, use the
PUSHW and POPW instructions to save and restore the A and T values.
Immediate before interrupt
SP 0280
H
Memory
x x
H
x x
H
x x
H
x x
H
027C
H
027D
H
027E
H
027F
H
x x
H
x x
H
0280
H
0281
H
Address
PC E000
H
PS 0870
H
Immediate after interrupt
PC E000
H
Memory
0 8
H
7 0
H
E 0
H
0 0
H
027C
H
027D
H
027E
H
027F
H
x x
H
x x
H
0280
H
0281
H
Address
PS 0870
H
SP 027C
H
}
}
PC
PS