MC68HC705C8ACS

Manufacturer Part NumberMC68HC705C8ACS
ManufacturerFreescale Semiconductor, Inc
MC68HC705C8ACS datasheet
 


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Freescale Semiconductor, Inc.
4.3.2 External Interrupt (IRQ)
An interrupt signal on the IRQ pin latches an external interrupt request.
After completing the current instruction, the CPU tests these bits:
Setting the I bit in the CCR disables external interrupts.
If the IRQ latch is set and the I bit is clear, the CPU then begins the
interrupt sequence. The CPU clears the IRQ latch while it fetches the
interrupt vector, so that another external interrupt request can be latched
during the interrupt service routine. As soon as the I bit is cleared during
the return-from-interrupt (RTI) instruction, the CPU can recognize the
new interrupt request.
Figure 4-1
shows an external interrupt timing diagram for the interrupt line. The
timing diagram illustrates two treatments of the interrupt line to the
processor.
1. Two single pulses on the interrupt line are spaced far enough
2. Many interrupt lines are “wire-ORed” to the IRQ line. If the interrupt
NOTE:
The internal interrupt latch is cleared in the first part of the interrupt
service routine. Therefore, a new external interrupt pulse could be
latched and serviced as soon as the I bit is cleared.
If the IRQ pin is not in use, connect it to the V
MC68HC705C8A — Rev. 3
MOTOROLA
For More Information On This Product,
IRQ latch
I bit in the CCR
Figure 4-1
shows the logic for external interrupts.
shows an external interrupt functional diagram.
apart to be serviced. The minimum time between pulses is a
function of the length of the interrupt service.
Once a pulse occurs, the next pulse normally should not occur
until an RTI occurs. This time (t
instruction cycles to the total number of cycles needed to complete
the service routine (not including the RTI instruction).
line remains low after servicing an interrupt, then the CPU
continues to recognize an interrupt.
Interrupts
Go to: www.freescale.com
Interrupts
Interrupt Sources
Figure 4-2
) is obtained by adding 19
ILIL
pin.
DD
Technical Data