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MSM80C154S/83C154S/85C154HVS
348
89. RETI (Return from interrupt routine)
00110010
70
Instruction code
Operations
Number of bytes
Number of cycles
Flags
(PSW)
Description
: Byte 1
(PC
8~15)←((SP))
(SP)←(SP)–1
(PC
0~7)←((SP))
(SP)←(SP)–1
*INTERRUPT ENABLE
:
C AC F0 RS1 RS0 OV F1 P
:
:
:
This return instruction functions as an interrupt routine terminat-
ing instruction. If a priority interrupt is generated while a non
priority interrupt routine is being executed, the CPU commences
to process the priority interrupt. And once processing of this
interrupt is commenced, no other interrupts can be processed
until the RETI instruction is executed.
Stack contents addressed by the stack pointer are popped in
the upper order 8 thru 15 of the program counter, and the stack
pointer is decremented by 1. Then the stack contents address-
ed by the updated stack pointer are popped in the lower order 0
thru 7 of the program counter, again decrementing the stack
pointer by 1. The program counter is updated with the stack
contents, and control is shifted to the address after updating. If
a new interrupt is generated, the CPU commences to process
the interrupt.
:
1
2