Presentation 12007

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The 8051 MICROCONTROLLER

Instruction set ……..

By:-Hitesh TejwaniGurpreet Kaur RaiAbhinav Biyani



The C8051 instructions are divided into five

functionalgroups:

Arithmetic operations

Logical operations

Data transfer operationsBoolean variable operations

Program branching operations



With arithmetic instructions, the C8051 CPU hasno special knowledge of the dataformat (e.g.signed/unsigned binary, binary coded decimal,ASCII, etc.)

The appropriate status bits in the PSW are setwhen specific conditions are met,which allows theuser software to manage the different data formats(carry, overflow etc…)

[@Ri] implies contents of memory location pointedto by R0 or R1

Rn refers to registers R0-R7 of the currentlyselected register



ADD

8-bit addition between the accumulator (A) and asecond operand.

The result is always in the accumulator.

The CY flag is set/reset appropriately.

ADDC

8-bit addition between the accumulator, a secondoperand and the previous value of the CY flag.

Useful for 16-bit addition in two steps.

The CY flag is set/reset appropriately.



Add 1E44H to 56CAH

CLR C ; Clear the CY flagMOV A, 44H ; The lower 8-bits of the 1st number

ADD A, CAH ; The lower 8-bits of the 2nd

numberMOV R1, A ; The result 0EH will be in R1. CY =

1.MOV A, 1EH ; The upper 8-bits of the 1st numberADDC A, 56H ; The upper 8-bits of the 2nd

numberMOV R2, A ; The result of the addition is 75H

The overall result: 750EH will be in R2:R1. CY = 0.



DA Decimal adjust the accumulator. Format the accumulator into a proper 2 digit packed BCD

number. Operates only on the accumulator. Works only after the ADD instruction.

SUBB Subtract with Borrow.

Subtract an operand and the previous value of the borrow(carry) flag from the accumulator. A A - <operand> - CY. The result is always saved in the accumulator. The CY flag is set/reset appropriately.



INC Increment the operand by one. The operand can be a register, a direct address, an indirect

address, the data pointer.

DEC Decrement the operand by one. The operand can be a register, a direct address, an indirect

address.

MUL AB / DIV AB Multiply A by B and place result in A:B. Divide A by B and place result in A:B.



Logical instructions perform Boolean operations(AND, OR, XOR, and NOT) on data bytes on a bit-by-bit

basis.

CPL / CLR Complement / Clear.Work on the accumulator or a bit.

CLR P1.2



RR – RL – RRC – RLC A

EXAMPLE:RR A

RR:

RRC:

RL:

RLC:

C

C





CLR - clear

RL – rotate left

RLC – rotate left through Carry

RR – rotate right

RRC – rotate right through Carry

SWAP – swap accumulator nibbles





PUSH / POP

Push and Pop a data byte onto the stack. The data byte is identified by a direct address from

the internal RAM locations. XCH

Exchange accumulator and a byte variable

XCH A, Rn XCH A, direct XCH A, @Ri

XCHD

Exchange lower digit of accumulator with the lower digit of thememory location specified. XCHD A, @Ri

The lower 4-bits of the accumulator are exchanged with the lower 4-bits of the internal memory location identified indirectly by theindex register.

The upper 4-bits of each are not modified.





Program branching instructions are used tocontrol the flow of program execution

Some instructions provide decision makingcapabilities before transferring control to otherparts of the program (conditional branches).





JZ Jump if A=0

JNZ Jump if A/=0

DJNZ Decrement and jump if A/=0

CJNE A,byte Jump if A/=byte

CJNE reg,#data Jump if byte/=#data

JC Jump if CY=1

JNC Jump if CY=0

JB Jump if bit=1

JNB Jump if bit=0

JBC Jump if bit=1 and clear bit



The 8051 provides 2 forms for the CALLinstruction:

Absolute Call – ACALL

Uses an 11-bit address similar to AJMP The subroutine must be within the same 2K page.

Long Call – LCALL

Uses a 16-bit address similar to LJMP

The subroutine can be anywhere.

Both forms push the 16-bit address of the nextinstruction on the stack and update the stack pointer.



Return is also similar to a jump, but

Return instruction pops PC from stack to get addressto jump to

ret ; PC stack



Another control transfer instruction is the CALL instruction,

which is used to call a subroutine.

LCALL(long call)This 3-byte instruction can be used to call

subroutines located anywhere within the 64K byte

address space of the 8051.

• ACALL (absolute call)

ACALL is 2-byte instruction. the targetaddress of the subroutine must be within 2K

byte range.



Main: ...

acall sublabel

...

...

sublabel:...

...

ret

the subroutine

call to the subroutine



Subroutines allow us to have "structured"assembly language programs.

This is useful for breaking a large design into

manageable parts. It saves code space when subroutines can be

called many times in the same program.



ACALL: Absolute Call

ADD, ADDC: Add Acc. (With Carry)

AJMP: Absolute Jump

ANL: Bitwise AND

CJNE: Compare & Jump if Not Equal

CLR: Clear Register

CPL: Complement Register

DA: Decimal Adjust

DEC: Decrement Register

DIV: Divide Accumulator by B

DJNZ: Dec. Reg. & Jump if Not Zero

INC: Increment Register

JB: Jump if Bit Set

JBC: Jump if Bit Set and Clear Bit

JC: Jump if Carry Set

JMP: Jump to Address

JNB: Jump if Bit Not Set

JNC: Jump if Carry Not Set

JNZ: Jump if Acc. Not Zero

JZ: Jump if Accumulator Zero

LCALL: Long Call

LJMP: Long Jump

MOV: Move Memory

MOVC: Move Code Memory

MOVX: Move Extended Memory

MUL: Multiply Accumulator by B

NOP: No Operation

ORL: Bitwise OR

POP: Pop Value From Stack

PUSH: Push Value Onto Stack

RET: Return From Subroutine

RETI: Return From Interrupt

RL: Rotate Accumulator Left

RLC: Rotate Acc. Left Through Carry

RR: Rotate Accumulator Right

RRC: Rotate Acc. Right Through Carry

SETB: Set Bit

SJMP: Short Jump

SUBB: Sub. From Acc. With Borrow

SWAP: Swap Accumulator Nibbles

XCH: Exchange Bytes

XCHD: Exchange Digits

XRL: Bitwise Exclusive OR

Undefined: Undefined Instruction



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Presentation 12007