INSTRUCTION SETS3F80JB

EI — Enable Interrupts

EI

Operation: SYM (0) 1

An EI instruction sets bit zero of the system mode register, SYM.0 to "1". This allows interrupts to be serviced as they occur (assuming they have highest priority). If an interrupt's pending bit was set while interrupt processing was disabled (by executing a DI instruction), it will be serviced when you execute the EI instruction.

Flags:

No flags are affected.

 

 

 

Format:

 

 

 

 

 

 

 

 

 

 

Bytes

Cycles

Opcode

 

 

 

 

 

 

(Hex)

 

 

opc

 

1

4

9F

Example:

Given: SYM = 00H:

 

 

 

 

EI

 

 

 

If the SYM register contains the value 00H, that is, if interrupts are currently disabled, the statement "EI" sets the SYM register to 01H, enabling all interrupts. (SYM.0 is the enable bit for global interrupt processing.)

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Image 168
Samsung S3F80JB manual EI Enable Interrupts, Operation SYM 0 ←