External Interrupt (IRQ)
Functional Description
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA External Interrupt (IRQ) 331
The external interrupt pins are falling-edge-triggered and are
software-configurable to be both falling-edge and low-level-triggered.
The MODE1 bit in the ISCR controls the triggering sensitivity of the
IRQ pin.
When the interrupt pin is edge-triggered only, the i nterrupt latch rem ains
set until a vector fetch, software clear, or reset occurs.
When the interrupt pin is both falling-edge and low-level-triggered, the
interrupt latch remains set until both of these occur:
Vector fetch, software clear, or reset
Return of the interrupt pin to logic 1
The vector fetch or software clear can occur before or af ter the in terrupt
pin returns to logic 1. As long as the pin is low, the interrupt request
remains pending.
When set, the IMASK1 bit in the ISCR masks all external interrupt
requests. A latched interrupt request is not presented to the interrupt
priority logic unless the IMASK bit is cl ear.
NOTE: The interrupt mask (I) in the condition code register (CCR) masks all
interrupt requests, including external interrupt requests.
(See Figure 17-3.)