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Microcontroladores 8051

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10.1. 8051 Microcontroller Instruction Set

10.1.1. ACALL addr11

Function: Absolute Call

Description:

ACALL unconditionally calls a subroutine located at the indicated address. The instruction increments the PC twice to obtain the address of the following instruction, then pushes the 16-bit result onto the stack (low-order byte first) and increments the Stack Pointer twice. The destination address is obtained by successively concatenating the five high-order bits of the incremented PC, opcode bits 7 through 5, and the second byte of the instruction. The subroutine called must therefore start within the same 2 K block of the program memory as the first byte of the instruction following ACALL. No flags are affected.

Example:

Initially SP equals 07H. The label SUBRTN is at program memory location 0345 H. After executing the following instruction,

ACALL SUBRTN

at location 0123H, SP contains 09H, internal RAM locations 08H and 09H will contain 25H and 01H, respectively, and the PC contains 0345H.

Bytes: 2

Cycles: 2

Encoding:

a10 a9 a8 1 0 0 0 1 , a7 a6 a5 a4 a3 a2 a1 a0

Operation: ACALL

(PC) ← (PC) + 2
(SP) ← (SP) + 1
((SP)) ← (PC7-0)
(SP) ← (SP) + 1
((SP)) ← (PC15-8)
(PC10-0) ← page address

10.1.2. ADD A,"src-byte"

Function: Add

Description:

ADD adds the byte variable indicated to the Accumulator, leaving the result in the Accumulator. The carry and auxiliary-carry flags are set, respectively, if there is a carry-out from bit 7 or bit 3, and cleared otherwise. When adding unsigned integers, the carry flag indicates an overflow occurred.

OV is set if there is a carry-out of bit 6 but not out of bit 7, or a carry-out of bit 7 but not bit 6; otherwise, OV is cleared. When adding signed integers, OV indicates a negative number produced as the sum of two positive operands, or a positive sum from two negative operands.

Four source operand addressing modes are allowed: register, direct, register-indirect, or immediate.

Example:

The Accumulator holds 0C3H (1100001lB), and register 0 holds 0AAH (10101010B). The following instruction,

ADD A,R0

leaves 6DH (01101101B) in the Accumulator with the AC flag cleared and both the carry flag and OV set to 1.

ADD A,Rn

Bytes: 1

Cycles: 1

Encoding:

0 0 1 0 1 r r r

Operation: ADD

(A) <- (A) + (Rn)

ADD A,direct

Bytes: 2

Cycles: 1

Encoding:

0 0 1 0 0 1 0 1 , direct address

Operation: ADD

(A) <- (A) + (direct)

ADD A,@Ri

Bytes: 1

Cycles: 1

Encoding:

0 0 1 0 0 1 1 i

Operation: ADD

(A) <- (A) + ((Ri))

ADD A,#data

Bytes: 2

Cycles: 1

Encoding:

0 0 1 0 0 1 0 0 , immediate data

Operation: ADD

(A) <- (A) + #data

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