MC68HC705C8A_13 Datasheet, PDF(51/222 Page) Freescale Semiconductor, Inc – Technical Data

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

MC68HC705C8A_13 Datasheet, PDF (51/222 Pages) Freescale Semiconductor, Inc – Technical Data

◁

Freescale Semiconductor, Inc.

Interrupts

Interrupt Sources

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:

â¢ IRQ latch

â¢ I bit in the CCR

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 the logic for external interrupts.

Figure 4-1 shows an external interrupt functional diagram. Figure 4-2

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

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 (tILIL) is obtained by adding 19

instruction cycles to the total number of cycles needed to complete

the service routine (not including the RTI instruction).

2. Many interrupt lines are âwire-ORedâ to the IRQ line. If the interrupt

line remains low after servicing an interrupt, then the CPU

continues to recognize an 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 VDD pin.

MC68HC705C8A â Rev. 3

MOTOROLA

Interrupts

For More Information On This Product,

Go to: www.freescale.com

Technical Data

▷