NEC PD75P402, PD75402A user manual Interrupt INTxxx generation

CHAPTER 6. INTERRUPT FUNCTIONS

6.5MACHINE CYCLES BEFORE INTERRUPT SERVICING

On the 75X, the machine cycles from the setting of the interrupt request flag (IRQn) until execution of the interrupt routine program are as shown below.

(1) When IRQn is set during execution of an interrupt control instruction

When IRQn is set during execution of an interrupt control instruction, the interrupt routine program is executed after 3 machine cycles of interrupt servicing have been performed following execution of the next instruction.

Interrupt (INTxxx) generation

A

B

C

D

A : Setting of IRQn

B : Execution of next instruction (between 1 and 3 machine cycles depending on instruction)

C : Interrupt servicing (3 machine cycles)

D : Execution of interrupt routine

Remarks 1. An interrupt control instruction is an instruction which manipulates interrupt-related hardware (data memory FB×H address). These instructions comprise the DI and EI instructions.

2.The 3 machine cycles of interrupt servicing include the time for manipulation of the stack on acknowledgment of an interrupt, etc.

Note 1. If there are a number of consecutive interrupt control instructions, the interrupt routine program is executed after 3 machine cycles of interrupt servicing have been performed following execution of the instruction which follows the last interrupt control instruction executed.

2.When IRQn is set, or when the interrupt control instruction executed thereafter is a DI instruction, the interrupt request by which IRQn was set is held pending.

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