Zilog Z16F2810 Manual de usuario descargar pdf (Pagina 126)

IRET Instruction UM018809-0611

110

ZNEO

CPU Core

User Manual

IRET

Definition

Interrupt Return

Syntax

IRET

Operation

Normal IRET Chained IRET

PC  (SP) PC  Pending Interrupt Vector

 SP + 4 FLAGS[0]  0

FLAGS[7:0]

 +1(SP)

 SP + 2

Description

This instruction is issued at the end of an interrupt service routine. It performs one of the follow-

ing two operations:

•

If no interrupts are pending or the Chained Interrupt Enable flag (CIRQE) is 0, execu-

tion of IRET restores the Program Counter and the Flags register from the stack.

•

If one or more vectored interrupts are pending and the CIRQE flag is 1, executing the

IRET instruction passes execution directly to the highest-priority pending interrupt

service routine. The contents of the stack are not changed.

For details about chained interrupts, see the Returning From a Vectored Interrupt

section on

page 44.

Any Push or other instructions in the service routine that decrement the stack pointer

must be followed by matching Pop or increment instructions to ensure the Stack Pointer

is at the correct location when IRET is executed. Otherwise, the wrong address loads into

the Program Counter and the program cannot operate properly.

Flags

If IRET executes normally, it restores the Flags register to its state prior to the first interrupt in

the chain.

Caution:

1 2 ... 121 122 123 124 125 126 127 128 129 130 131 ... 215 216

Sin comentarios

Zilog Z16F2810 Manual de usuario Pagina 126