EI

EI

Enable Interrupts (AGU)

Operation

Assembler Syntax

0 → DI

EI

Description

 

EI

 

EI

Clears the DI bit in the status register to enable interrupts. The EI instruction and its counterpart, the DI instruction, can be used to delimit a non-interruptible code sequence. For example, a non-interruptible read-modify-write sequence of execution sets can be written like this:

DI read modify EI write

Where read, modify, and write represent instruction(s). This instruction can appear only once in an execution set. The effect of EI may not be immediate. That is, a pending interrupt may not be serviced as the first execution set immediately after this instruction because of pipeline effects.

Status and Conditions that Affect Instruction

Register Address

Bit Name

Description

SR[18]

EXP

Determines execution working mode.

Status and Conditions Changed by Instruction

Register Address

Bit Name

Description

SR[19]

DI

Clears disable interrupt bit.

Example

ei

Register/Memory Address

SR

Before

$EC0000

After

$E40000

Instruction Formats and Opcodes

Instruction

Words

Cycles

Type

EI

1

1

4

Opcode

15

8

7

0

1 0 0 1 1 1 1 1 0 1 1 1 1 1 0 0

SC140 DSP Core Reference Manual

A-163

Page 477
Image 477
Freescale Semiconductor SC140 specifications → Di, SR19 Clears disable interrupt bit