
MB89630 SERIES HARDWARE MANUAL
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(3) Description of operation
Interrupt functions
The MB89630 series of microcontrollers have 12 inputs for interrupt requests from each resource. The
interrupt level is set by 2-bit registers corresponding to each input. When an interrupt is requested from a
resource, the interrupt controller receives it and transfers the contents of the corresponding register to the
CPU. The interrupt to the device is processed as follows:
1) An interrupt source is generated inside each resource.
2) If an interrupt is enabled, an interrupt request is output from each resource to the interrupt controller by
referring to the interrupt-enable bit inside each resource.
3) After receiving this interrupt request, the interrupt controller determines the priority of simultaneously-
requested interrupts and then transfers the interrupt level for the applicable interrupt to the CPU.
4) The CPU compares the interrupt level requested from the interrupt controller with the IL bit in the proc
essor status register.
5) As a result of the comparison, if the priority of the interrupt level is higher than that of the current inter
rupt processing level, the contents of the I-flag in the same processor status register are checked.
6) As a result of the check in step (5), if the I-flag is enabled for an interrupt, the contents of the IL bit are
set to the required level. As soon as the currently-executing instruction is terminated, the CPU performs
the interrupt processing and transfers control to the interrupt-processing routine.
7) When an interrupt source is cleared by software in the user's interrupt processing routine, the CPU ter-
minates the interrupt processing.
Figure 2.8 outlines the interrupt operation for the MB89630 series of microcontrollers.
Fig. 2.8 Interrupt-processing Flowchart