STC89LE53RC datasheet(71/165 Pages) STC

71 / 165 page

RETI

Function:

Return from interrupt

Description:

RETI pops the high- and low-order bytes of the PC successively from the stack, and restores

the interrupt logic to accept additional interrupts at the same priority level as the one just

processed. The Stack Pointer is left decremented by two. No other registers are affected; the

PSW is not automatically restored to its pre-interrupt status. Program execution continues at

the resulting address, which is generally the instruction immediately after the point at which

the interrupt request was detected. If a lower- or same-level interrupt had been pending when

the RETI instruction is executed, that one instruction will be executed before the pending

interrupt is processed.

Example:

The Stack Pointer originally contains the value 0BH. An interrupt was detected during the

instruction ending at location 0122H. Internal RAM locations 0AH and 0BH contain the

values 23H and 01H, respectively. The instruction,

RETI

will leave the Stack Pointer equal to 09H and return program execution to location 0123H.

Bytes:

Cycles:

Encoding:

0 0 1 1

0 0 1 0

Operation:

RETI

(PC

15-8) ← ((SP))

← ((SP))

((SP))

(SP) ← (SP) -1

← (SP) -1

(SP) -1

(PC

7-0) ← ((SP))

← ((SP))

((SP))

(SP) ← (SP) -1

← (SP) -1

(SP) -1

RL A

Function:

Rotate Accumulator Left

Description:

The eight bits in the Accumulator are rotated one bit to the left. Bit 7 is rotated into the bit 0

position. No flags are affected.

Example:

The Accumulator holds the value 0C5H (11000101B). The instruction,

leaves the Accumulator holding the value 8BH (10001011B) with the carry unaffected.

Bytes:

Cycles:

Encoding:

0 0 1 0

0 0 1 1

Operation:

(An

+1) ← (A

← (A

(An) n = 0-6

(A0) ← (A

← (A

(A7)

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