Software Interrupt; Overview; Structure - Fujitsu F2MC-16LX MB90580 Series Hardware Manual

7.5 Software Interrupt

7.5 Software Interrupt

7.5.1 Overview

In response to execution of a special instruction, control is transferred from the program currently executed
by the CPU to the interrupt processing program defined by the user. This is called the software interrupt
function. A software interrupt occurs always when the software interrupt instruction is executed. The CPU
performs the following processing when a software interrupt occurs:
Saves the values in the PC, PS, AH, AL, PCB, DTB, ADB, and DPR registers of the CPU to the
system stack.
Sets I in the PS register. Interrupts are automatically disabled.
Fetches the corresponding interrupt vector value, then branches to the processing indicated by that
value.
A software interrupt request issued by the INT instruction has no interrupt request or enable flag. A
software interrupt request is always issued by executing the INT instruction.
The INT instruction does not have an interrupt level. Therefore, the INT instruction does not update ILM.
The INT instruction clears the I flag to suspend subsequent interrupt requests.

7.5.2 Structure

Software interrupts are handled within the CPU:
CPU ...........................
As shown in Table 7.3a, software interrupts share the same interrupt vector area with hardware interrupts.
For example, interrupt request number INT 13 is used for external interrupt #0 of a hardware interrupt as
well as for INT #13 of a software interrupt. Therefore, external interrupt #0 and INT #13 call the same inter-
rupt processing routine.
88 Chapter 7: Interrupt
Microcode: Interrupt processing step
MB90580 Series