68HC705PD6 datasheet(35/165 Pages) MOTOROLA

35 / 165 page

July 7, 1997

GENERAL RELEASE SPECIFICATION

MC68HC05PD6

INTERRUPTS

MOTOROLA

REV 1.1

4-1

SECTION 4

INTERRUPTS

The MCU can be interrupted in seven different ways:

•

Non-maskable Software Interrupt Instruction (SWI)

•

P-Decoder Interrupt

•

External Interrupt (IRQ)

•

Key Wake-Up Interrupt (KWI)

•

Timer Interrupt

•

SCI Interrupt

•

RTC Interrupt

4.1

CPU INTERRUPT PROCESSING

Interrupts cause the processor to save register contents on the stack and to set the

interrupt mask (I-bit) to prevent additional interrupts. Unlike RESET, hardware interrupts

do not cause the current instruction execution to be halted, but are considered pending

until the current instruction is complete.

If interrupts are not masked (I-bit in the CCR is cleared) and the corresponding interrupt

enable bit is set the processor will proceed with interrupt processing. Otherwise, the next

instruction is fetched and executed. If an interrupt occurs the processor completes the

current instruction, then stacks the current CPU register states, sets the I-bit to inhibit

further interrupts, and finally checks the pending hardware interrupts. If more than one

interrupt is pending following the stacking operation, the interrupt with the highest vector

location shown in Table 4-1 will be serviced first. The SWI is executed the same as any

other instruction, regardless of the I-bit state.

When an interrupt is to be processed the CPU fetches the address of the appropriate

interrupt software service routine from the vector table at locations $FFF0 thru $FFFF as

defined in Table 4-1.

An RTI instruction is used to signify when the interrupt software service routine is

completed. The RTI instruction causes the register contents to be recovered from the

stack and normal processing to resume at the next instruction that was to be executed

when the interrupt took place. Figure 4-1 shows the sequence of events that occur during

interrupt processing.

68HC705PD6 Datasheet(PDF) 35 Page - Motorola, Inc

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