UPD17708 datasheet(137/356 Pages) NEC

137 / 356 page

137

µPD17704, 17705, 17707, 17708, 17709

12.4 Stack Pointer, Address Stack Registers, and Program Counter

The address stack registers save a return address when execution returns from an interrupt routine.

The stack pointer specifies the address of an address stack register.

When an interrupt is accepted, the value of the stack pointer is decremented by one, and the value of the

program counter at that time is saved to an address stack register specified by the stack pointer.

Next, the interrupt routine is executed. When the interrupt return (RETI) instruction is executed after that,

the contents of an address stack register specified by the stack pointer are restored to the program counter,

and the value of the stack pointer is incremented by one.

For further information, also refer to 3. ADDRESS STACK (ASK).

12.5 Interrupt Enable Flip-Flop (INTE)

The interrupt enable flip-flop enables or disables the 12 types of maskable interrupts.

When this flip-flop is set, all the interrupts are enabled. When it is reset, all the interrupts are disabled.

This flip-flop is set or reset by dedicated instructions EI (to set) and DI (to reset).

The EI instruction sets this flip-flop when the instruction next to EI is executed, and the DI instruction resets

the flip-flop while it is being executed.

When an interrupt is accepted, this flip-flop is automatically reset.

This flip-flop is also reset at power-ON reset, at a reset by the RESET pin, at a watchdog timer, overflow or

underflow of the stack, and at CE reset. The flip-flop retains the previous status on execution of the clock stop

instruction.

UPD17708 Datasheet(PDF) 137 Page - NEC