Stack Operation During Interrupt Processing - Fujitsu MB95630H Series Hardware Manual

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MB95630H Series

Stack Operation During Interrupt Processing

This section describes how the contents of a register are saved and restored

during interrupt processing.

■ Stack Operation at the Start of Interrupt Processing

Once the CPU accepts an interrupt, it automatically saves the current value of the program

counter (PC) and that of the program status (PS) values to the stack.

Figure 5.1-4 shows the stack operation at the start of interrupt processing.

Figure 5.1-4 Stack Operation at Start of Interrupt Processing

Immediately before interrupt

■ Stack Operation after Returning from Interrupt

When the CPU executes the interrupt return instruction (RETI) at the end of interrupt

processing, it restores from the stack the value of the program status (PS) first and that of the

program counter (PC), which is opposite to the sequence of saving the two values to the stack.

After the restoration, both PS and PC return to their states before the start of interrupt

Since the value of the accumulator (A) and that of the temporary accumulator (T) are not

automatically saved to the stack, use the PUSHW and POPW instructions to save and

restore the values of A and T.

MN702-00009-1v0-E

FUJITSU SEMICONDUCTOR LIMITED

CHAPTER 5 INTERRUPTS

Immediately after interrupt

5.1 Interrupts