MC9S08AC60 Datasheet, PDF (69/348 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 5 Resets, Interrupts, and System Configuration
5.5.2 External Interrupt Request (IRQ) Pin
External interrupts are managed by the IRQSC status and control register. When the IRQ function is
enabled, synchronous logic monitors the pin for edge-only or edge-and-level events. When the MCU is in
stop mode and system clocks are shut down, a separate asynchronous path is used so the IRQ (if enabled)
can wake the MCU.
5.5.2.1 Pin Configuration Options
The IRQ pin enable (IRQPE) control bit in the IRQSC register must be 1 in order for the IRQ pin to act as
the interrupt request (IRQ) input. As an IRQ input, the user can choose the polarity of edges or levels
detected (IRQEDG), whether the pin detects edges-only or edges and levels (IRQMOD), and whether an
event causes an interrupt or only sets the IRQF flag which can be polled by software.
The IRQ pin, when enabled, defaults to use an internal pull device (IRQPDD = 0), configured as a pull-up
or pull-down depending on the polarity chosen. If the user desires to use an external pull-up or pull-down,
the IRQPDD can be written to a 1 to turn off the internal device.
BIH and BIL instructions may be used to detect the level on the IRQ pin when the pin is configured to act
as the IRQ input.
NOTE
• The voltage measured on the pulled up IRQ pin may be as low as
V_DD-0.7 V. The internal gates connected to this pin are pulled all the
way to V_DD. All other pins with the enabled pullup resistor will have an
unloaded measurement of V_DD.
• When enabling the IRQ pin for use, the IRQF will be set, and should be
cleared prior to enabling the interrupt. When configuring the pin for
falling edge and level sensitivity in a 5V system, it is necessary to wait
at least 6 cycles between clearing the flag and enabling the interrupt.
5.5.2.2 Edge and Level Sensitivity
The IRQMOD control bit reconfigures the detection logic so it detects edge events and pin levels. In this
edge detection mode, the IRQF status flag becomes set when an edge is detected (when the IRQ pin
changes from the deasserted to the asserted level), but the flag is continuously set (and cannot be cleared)
as long as the IRQ pin remains at the asserted level.
5.5.3 Interrupt Vectors, Sources, and Local Masks
Table 5-2 provides a summary of all interrupt sources. Higher-priority sources are located toward the
bottom of the table. The high-order byte of the address for the interrupt service routine is located at the
first address in the vector address column, and the low-order byte of the address for the interrupt service
routine is located at the next higher address.
When an interrupt condition occurs, an associated flag bit becomes set. If the associated local interrupt
enable is 1, an interrupt request is sent to the CPU. Within the CPU, if the global interrupt mask (I bit in
the CCR) is 0, the CPU will finish the current instruction, stack the PCL, PCH, X, A, and CCR CPU
MC9S08AC60 Series Data Sheet, Rev. 2
Freescale Semiconductor
69