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CPU

User Manual

UM001604-0108 Interrupts

108

longest instruction present in the application program + 2T

C (internal synchronization

time).

Nesting of Vectored Interrupts

Nesting of vectored interrupts allows higher priority requests to interrupt a lower priority

request. To initiate vectored interrupt nesting, do the following during the interrupt service

routine:

•

Push the old IMR on the stack

•

Load IMR with a new mask to disable lower priority interrupts

•

Execute EI instruction

•

Proceed with interrupt processing

•

After processing is complete, execute DI instruction

•

Restore the IMR to its original value by returning the previous mask from the stack

•

Execute IRET

Depending on the application, some simplification of the above procedure may be possi-

ble.

Polled Processing

Polled interrupt processing is supported by masking off the IRQ to be polled. This is

accomplished by clearing the corresponding bits in the IMR.

To enable any interrupt, first the interrupt mechanism must be engaged with an EI instruc-

tion. If only polled interrupts are to be serviced, execute:

Figure 102. Z8 Interrupt Acknowledge Timing

For Stack External Only

PC+1

PCLSP-1

SP-2

PCH SP-3 FLAGS

VECT

VECT+1

Even Vector Address

Odd Vector Address

Op Code (Discarded)

VECTH

VECTL

First Instruction Of Interrupt Service Routine

For Stack External Only

A0-A7 IN

Internal Clock

/DS

A0-A7 OUT

Stack Push

Fetch

Vector High

Fetch

Vector Low

Stack Push Stack Push

R/W

1 2 ... 110 111 112 113 114 115 116 117 118 119 120 ... 259 260

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