External Interrupt (IRQ)

Interrupt signals on the IRQ pin are latched into the IRQ1 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 latch that caused the vector fetch.

•Software clear — Software can clear an interrupt latch by writing to the appropriate acknowledge bit in the interrupt status and control register (ISCR). Writing a logic 1 to the ACK1 bit clears the IRQ1 latch.

•Reset — A reset automatically clears both interrupt latches.

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 interrupt latch remains 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 after the interrupt 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 clear.

NOTE

The interrupt mask (I) in the condition code register (CCR) masks all interrupt requests, including external interrupt requests. (See Figure 8-3.)

8.4 IRQ Pin

A logic 0 on the IRQ pin can latch an interrupt request into the IRQ latch. A vector fetch, software clear, or reset clears the IRQ latch.

If the MODE1 bit is set, the IRQ pin is both falling-edge-sensitive and low-level- sensitive. With MODE1 set, both of these actions must occur to clear the IRQ1 latch:

•Vector fetch, software clear, or reset — A vector fetch generates an interrupt acknowledge signal to clear the latch. Software can generate the interrupt acknowledge signal by writing a logic 1 to the ACK1 bit in the interrupt status and control register (ISCR). The ACK1 bit is useful in applications that poll the IRQ pin and require software to clear the IRQ1 latch. Writing to the ACK1 bit can also prevent spurious interrupts due to noise. Setting ACK1 does not affect subsequent transitions on the IRQ pin. A falling edge that occurs after writing to the ACK1 bit latches another interrupt request. If the IRQ1 mask bit, IMASK1, is clear, the CPU loads the program counter with the vector address at locations $FFFA and $FFFB.

•Return of the IRQ pin to logic 1 — As long as the IRQ pin is at logic 0, the IRQ1 latch remains set.

MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1

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Freescale Semiconductor MC68HC908MR32, MC68HC908MR16 manual IRQ Pin, External Interrupt IRQ
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MC68HC908MR16, MC68HC908MR32 specifications

Freescale Semiconductor's MC68HC908MR32 and MC68HC908MR16 microcontrollers are part of the popular HC08 family, designed primarily for embedded applications. These microcontrollers are particularly favored in automotive, industrial, and consumer product sectors due to their reliability and versatility.

One of the standout features of the MC68HC908MR series is its CMOS technology, which enhances performance while minimizing power consumption. This makes these microcontrollers suitable for battery-operated devices. They operate at a maximum clock frequency of 2 MHz and offer a 16-bit architecture, providing a solid balance between processing power and efficiency.

The MC68HC908MR32 variant is equipped with 32KB of flash memory, which allows for the storage of complex programs and extensive data handling. In contrast, the MC68HC908MR16 features 16KB of flash memory, making it ideal for simpler applications. Both microcontrollers also come with 1KB of RAM, enabling efficient data processing and real-time operations.

Another significant characteristic of these microcontrollers is their integrated peripherals. They come with multiple input/output (I/O) pins, which allow for connectivity with various sensors and actuators. The built-in timer systems offer precise timing control for automotive and industrial applications, while the Analog-to-Digital Converter (ADC) provides essential conversion capabilities for various analog signals.

For communication purposes, the MC68HC908MR series includes a serial communication interface, enabling easy integration with other devices and systems. This versatility facilitates the development of complex systems that require interaction with external components.

Security is another crucial aspect of these microcontrollers. They have built-in fail-safe mechanisms to ensure reliable operation under various conditions, making them suitable for critical systems. Additionally, their robust architecture helps to safeguard against potential disruptions or attacks.

In summary, Freescale Semiconductor's MC68HC908MR32 and MC68HC908MR16 microcontrollers are key players in the embedded systems landscape. Their blend of power efficiency, integrated features, and scalability ensures they remain relevant for a wide array of applications, making them a favored choice among engineers and developers looking for dependable solutions in a competitive market.
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