NEC PD75402A - Manual (Page 146)

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CHAPTER 6. INTERRUPT FUNCTIONS
6.5 MACHINE 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.
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.
A B C D
Interrupt
(INTxxx)
generation