Datasheet

Chapter 5 Resets, Interrupts, and General System Control

MC9S08QG8 and MC9S08QG4 Data Sheet, Rev. 5

Freescale Semiconductor 63

The IRQ pin, when enabled, defaults to use an internal pullup device (IRQPDD = 0). If the user desires to

use an external pullup, 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

This pin does not contain a clamp diode to V

and should not be driven

above V

The voltage measured on the internally pulled-up IRQ pin will not be pulled

to V

. The internal gates connected to this pin are pulled to V

. The IRQ

pullup should not be used to pull up components external to the MCU. The

internal gates connected to this pin are pulled all the way to V

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

registers; set the I bit; and then fetch the interrupt vector for the highest priority pending interrupt.

Processing then continues in the interrupt service routine.