UPD17073 NEC, UPD17073 Datasheet - Page 77

• Manufacturer Part Number: UPD17073
• Description: 4-BIT SINGLE-CHIP MICROCONTROLLER WITH HARDWARE FOR DIGITAL TUNING SYSTEM
• Manufacturer: NEC

11.7 Operations after Accepting Interrupt
not involve execution of an ordinary instruction. This instruction cycle is called an interrupt cycle.
an interrupt.
(1) The interrupt enable flip-flop and the interrupt request flag corresponding to the accepted interrupt request
(2) The contents of the stack pointer are decremented by one.
(3) The contents of the program counter are saved to the address stack register specified by the stack pointer.
(4) The lower 1 bit of the bank register (BANK) is saved to the interrupt stack.
(5) The contents of the vector address generator corresponding to the accepted interrupt are transferred to the
When an interrupt has been accepted, the following processing is automatically executed in sequence:
The above steps (1) through (5) are executed in one special instruction cycle (53.3 s: normal operation) that does
Therefore, it takes the CPU one instruction cycle to branch to the corresponding vector address after it has accepted
are cleared to “0”. Therefore, the interrupt is disabled.
At this time, the content of the program counter is the program memory address next to the one at which the
interrupt has been accepted.
For example, if the interrupt has been accepted while a branch instruction is executed, the branch destination
address is loaded to the program counter. If a subroutine call instruction is executed when the interrupt has
been accepted, the address that called the subroutine is loaded to the program counter. When the skip
condition of a skip instruction is satisfied, the next instruction is treated as a no-operation instruction (“NOP”)
and then the interrupt is accepted. Consequently, the contents of the program counter are the skipped address.
Caution At this time, the contents of the program status word (PSWORD) are not saved. Save the
program counter. Therefore, the execution branches to an interrupt service routine.
contents of the program status word by software as necessary.
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