MC68HC908JW32_09 Datasheet, PDF (185/232 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Chapter 14
External Interrupt (IRQ)
14.1 Introduction
The IRQ module provides two external interrupt inputs: one dedicated IRQ pin and one shared port pin,
PTE3/D–.
14.2 Features
Features of the IRQ module include:
• Two external interrupt pins, IRQ and PTE3/D–
• IRQ interrupt control bits
• Programmable edge-only or edge and level interrupt sensitivity
• Automatic interrupt acknowledge
• Low leakage IRQ pin for external RC wake up input
• Selectable internal pullup resistor
14.3 Functional Description
A logic 0 applied to the external interrupt pin can latch a CPU interrupt request. Figure 14-1 shows the
structure of the IRQ module.
Interrupt signals on the IRQ pin are latched into the IRQ latch. An interrupt latch remains set until one of
the following actions occurs:
• Vector fetch — A vector fetch automatically generates an interrupt acknowledge signal that clears
the IRQ latch.
• Software clear — Software can clear the interrupt latch by writing to the acknowledge bit in the
interrupt status and control register (ISCR). Writing a logic 1 to the ACK bit clears the IRQ latch.
• Reset — A reset automatically clears the interrupt latch.
The external interrupt pin is falling-edge-triggered and is software-configurable to be either falling-edge
or low-level-triggered. The MODE bit in the ISCR controls the triggering sensitivity of the IRQ pin.
When the interrupt pin is edge-triggered only, the CPU interrupt request remains set until a vector fetch,
software clear, or reset occurs.
When the interrupt pin is both falling-edge and low-level-triggered, the CPU interrupt request remains set
until both of the following occur:
• Vector fetch or software clear
• Return of the interrupt pin to logic one
The vector fetch or software clear may occur before or after the interrupt pin returns to logic 1. As long as
the pin is low, the interrupt request remains pending. A reset will clear the latch and the MODE control
bit, thereby clearing the interrupt even if the pin stays low.
MC68HC908JW32 Data Sheet, Rev. 6
Freescale Semiconductor
185