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CHAPTER 3 CPU
3.5.18
Stack Operation for Interrupt Processing
When an interrupt request is accepted, the values of dedicated registers are
automatically saved to the system stack before transition to interrupt processing. At
completion of interrupt processing, the values of the dedicated registers are
automatically returned from the system stack.
I Stack Operation at Starting Interrupt Processing
When an interrupt is accepted, the CPU automatically saves the values of the current-dedicated registers in
the system stack in the following order.
• Accumulator (AH, AL)
• Direct page register (DPR)
• Additional data bank register (ADB)
• Data bank register (DTB)
• Program bank register (PCB)
• Program counter (PC)
• Processor status (PS)
Figure 3.5-18 shows the stack operation at starting interrupt processing.
Figure 3.5-18 Stack Operation at Starting Interrupt Processing
Immediately-
preceding interrupt
SSB
00
H
08FE
SSP
H
0000
A
H
AH
01
DPR
H
00
DTB
H
PC
803F
H
20E0
PS
H
I Stack Operation at Return from Interrupt Processing
When the interrupt return instruction (RETI) is executed after completion of interrupt processing, the
values of the dedicated registers (PS, PC, PCB, DTB, ADB, DPR, AL, AH) are returned to each register
from the system stack, and the dedicated registers return to the condition before interrupt started.
92
Address
Memory
08F2
XX
H
H
XX
H
XX
H
XX
H
08FE
XX
H
H
XX
AL
H
XX
H
00
ADB
XX
H
H
XX
H
FF
PCB
XX
H
H
XX
H
XX
H
08FE
H
08FF
H
Byte
Immediately-after
interrupt
SSB
00
Lower
H
08F2
SSP
H
0000
A
H
AH
01
DPR
H
00
DTB
H
PC
803F
H
SP
20E0
PS
H
Upper
Address
Memory
08F2
E0
H
H
2 0
H
3F
H
8 0
H
08FE
FF
H
H
0 0
AL
H
0 0
H
00
0 1
ADB
H
H
FE
H
FF
PCB
0 8
H
H
0 0
H
0 0
H
08FE
H
08FF
H
Byte
SP after
updating
PS
PC
PCB
DTB
ADB
DPR
AL
AH
SP
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