Chapter 11
External Interrupt (IRQ)
11.1 Introduction
The IRQ (external interrupt) module provides a maskable interrupt input.
11.2 Features
Features of the IRQ module include the following:
• A dedicated external interrupt pin, IRQ
• IRQ interrupt control bits
• Hysteresis buffer
• Programmable edge-only or edge and level interrupt sensitivity
• Automatic interrupt acknowledge
• Selectable internal pullup resistor
11.3 Functional Description
A logic zero applied to the external interrupt pin can latch a CPU interrupt request.
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 (INTSCR). Writing a one 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 falling-edge and low-level-triggered. The MODE bit in the INTSCR 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
MC68HC908JL3E Family Data Sheet, Rev. 4
Freescale Semiconductor
113
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
