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CHAPTER 4 INTERRUPT PROCESSING
4.4 Multiple Interrupt
The F
2
MC-8FX CPU can have a maximum of four levels as maskable interrupts. These
can be used to assign priorities to interrupts from resources.
■ Multiple Interrupt
A specific example is given below.
• When giving priority over the A/D converter to the timer interrupt
When the above program is started, interrupts are generated from the A/D converter and timer after an
elapsed time. In this case, when the timer interrupt occurs while processing the A/D converter interrupt, it
will be processed through the sequence shown in Figure 4.4-1.
Figure 4.4-1 Example of Multiple Interrupt
When starting processing of an A/D converter interrupt, the IL bit in the PS register of the CPU is
automatically the same as the value of request (2 here). Therefore, when a level 1 or 0 interrupt request is
issued during the processing of an A/D converter interrupt, the processing proceeds without disabling the
A/D converter interrupt request. When temporarily disabling interrupts lower in priority than this interrupt
during A/D converter interrupt processing, disable the I flag in the PS register of the CPU for the interrupts
or set the IL bit to 0.
When control is returned to the interrupted routine by the release instruction after completion of each
interrupt processing routine, the PS register is set to the value saved in the stack. Consequently, the IL bit
takes on the value before interruption.
For actual coding, refer to the Hardware Manual for each device to check the addresses of the interrupt
controller and each resource and the interrupts to be supported.
START MOV ADIL, #2 Set the interrupt level of the A/D converter to 2.
MOV TMIL, #1 Set the interrupt level of the timer to 1. ADIL and
TMIL are IL bits in the interrupt controller.
CALL STAD Start the A/D converter.
CALL STTM Start the timer.
.
.
.
ı
ı
Main program
...
...
Initialize the resource.
The A/D converter
interrupt occurs.
The main program
is resumed.
A/D converter interrupt processing
IL=2
IL=1
Timer interrupt
occurs.
Suspended
Resumed
Process the A/D
converter interrupt.
Release the timer interrupt.
Process the timer interrupt.
Process the timer interrupt.
Release the timer interrupt.