External Interrupt Function - Fujitsu MB90420/5 (A) Series Hardware Manual

MB90420/5 (A) SERIES F

16.5.1 External Interrupt Function

The DTP/external interrupt circuit has the external interrupt function that issues an interrupt request by the
input of the selected signal level to the DTP/external interrupt pin.
n External interrupt function
When the signal (edge or level) selected by the interrupt request level setting register (ELVR) is detected at
the DTP/external interrupt pin, 1 is set for the ER7 to ER0 bits of the DTP/interrupt factor register (EIRR).
When the DTP/interrupt enable register interrupt request enable bits are already set (ENIR: EN7 to EN0 = 1)
at this point, the occurrence of the interrupt factor is notified to the interrupt controller. The interrupt
controller determines the interrupt level (ICR: IL2 to IL0) of the interrupt request issued from the other
resource and the priority of the two or more interrupts generated concurrently, etc. The CPU determines the
interrupt level of the interrupt level mask registers (PS: ILM2 to ILM0), strength of interrupt level and the
interrupt enable bit (PS: CCR: 1), etc. When the interrupt request is accepted by the CPU, interrupt
processing by the internal operation (microprogram) of the CPU is performed causing a branch to the
interrupt-processing routine. Write 0 to the corresponding interrupt request flag bit using the interrupt-
processing routine, to clear the interrupt request.
Notes: 1. When the DTP/external interrupt start factor is generated, the ER bit is set to 1 irrespective of the
state of the corresponding EN bit.
2. When the interrupt routine is started, clear the ER bit related to the interrupt start factor. Control
cannot be returned from the interrupt while the ER bit is set to 1. At this point, take care not to
clear flag bits not related to the interrupt factor unconditionally.
2
MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL
16-14