INSTRUCTION FORMAT
INSTRUCTION = command to the microcontroller Consists of op-code and operand Word size: one byte => includes the opcode and operand in the same byte
two byte =>first byte specifies the operation code
second byte specifies the operand three byte => the first byte specifies the opcode two bytes specify the 16-bit address
INSTRUCTION FORMAT
Data types and directives: DB => Define Byte => used to define data format 8051 supports decimal, hexadecimal, ASCII, and binary data Decimal D ASCII Binary B Eg: ADD A, #50 ; D is optional Eg: MOV A, #A Eg: MOV A, #01010000B
Hexadecimal H Eg: ADD A, #50H
INSTRUCTION FORMAT
Data types and directives: ORG ORIGIN Used to indicate the beginning of address
EQU EQUATE
Used to define constant without occupying a memory location Associates a constant value with a data label Wherever the label occurs the constant value is sustituted COUNT EQU 25 MOV R3, #COUNT
ADDRESSING MODES OF 8051
The 8051 provides a total of five distinct addressing modes. (1) immediate (2) register (3) direct (4) register indirect (5) indexed
ADDRESSING MODES OF 8051
Immediate Addressing Mode The operand comes immediately after the op-code. The immediate data must be preceded by the pound sign, "#"
ADDRESSING MODES OF 8051
Register Addressing Mode Register addressing mode involves the use of registers to hold the data to be manipulated
ADDRESSING MODES OF 8051
Direct Addressing Mode - It is most often used to access RAM locations 30 - 7FH. -This is due to the fact that register bank locations are accessed by the register names of R0 - R7. -There is no such name for other RAM locations so must use direct addressing -In the direct addressing mode, the data is in a RAM memory location whose address is known, and this address is given as a
part of the instruction
ADDRESSING MODES OF 8051
ADDRESSING MODES OF 8051
Register Indirect Addressing Mode A register is used as a pointer to the data. If the data is inside the CPU, only registers R0 and R 1 are used for this purpose. R2 - R7 cannot be used to hold the address of an operand located in RAM when using indirect addressing mode. When RO and R 1 are used as pointers they must be preceded by the @ sign.
ADDRESSING MODES OF 8051
ADDRESSING MODES OF 8051
Indexed Addressing Mode Indexed addressing mode is widely used in accessing data elements of look-up table entries located in the program ROM space of the 8051. The instruction used for this purpose is : MOVC A, @ A+DPTR
The 16-bit register DPTR and register A are used to form the
address of the data element stored in on-chip ROM.
ADDRESSING MODES OF 8051
Indexed Addressing Mode l Because the data elements are stored in the program (code) space ROM of the 8051, the instruction MOVC is used instead of MOV. The "C" means code. l In this instruction the contents of A are added to the 16-bit
register DPTR to form the 16- bit address of the needed data.
INSTRUCTION SET OF 8051
Depending on operation they perform, all instructions are divided in several groups: Arithmetic Instructions Branch Instructions Data Transfer Instructions
Logic Instructions
Bit-oriented Instructions
Arithmetic Instructions
ADD A,Rn Adds the register to the accumulator ADD A,direct Adds the direct byte to the accumulator ADD A,@Ri ADD A,#data ADDC A,Rn Adds the indirect RAM to the accumulator Adds the immediate data to the accumulator Adds the register to the accumulator with a carry flag
ADDC A,direct Adds the direct byte to the accumulator with a carry flag ADDC A,@Ri Adds the indirect RAM to the accumulator with a carry flag ADDC A,#data Adds the immediate data to the accumulator with a carry flag
Arithmetic Instructions
SUBB A,Rn Subtracts the register from the accumulator with a borrow
SUBB A,direct Subtracts the direct byte from the accumulator with a borrow SUBB A,@Ri Subtracts the indirect RAM from the accumulator with a borrow Subtracts the immediate data from the accumulator with a SUBB A,#data borrow INC A INC Rn INC Rx INC @Ri Increments the accumulator by 1 Increments the register by 1 Increments the direct byte by 1 Increments the indirect RAM by 1
Arithmetic Instructions
DEC A DEC Rn DEC Rx Decrements the accumulator by 1 Decrements the register by 1 Decrements the direct byte by 1
DEC @Ri
INC DPTR MUL AB DIV AB DA A
Decrements the indirect RAM by 1
Increments the Data Pointer by 1 Multiplies A and B Divides A by B Decimal adjustment of the accumulator according to BCD code
BRANCHING INSTRUCTIONS
ACALL addr11 Absolute subroutine call LCALL addr16 Long subroutine call RET Returns from subroutine
RETI
AJMP addr11 LJMP addr16 SJMP rel
Returns from interrupt subroutine
Absolute jump Long jump Short jump (from 128 to +127 locations relative to the following instruction)
BRANCHING INSTRUCTIONS
JC rel JNC rel
JB bit,rel JBC bit,rel JMP @A+DPTR JZ rel JNZ rel
Jump if carry flag is set. Short jump. Jump if carry flag is not set. Short jump.
Jump if direct bit is set. Short jump. Jump if direct bit is set and clears bit. Short jump. Jump indirect relative to the DPTR Jump if the accumulator is zero. Short jump. Jump if the accumulator is not zero. Short jump.
BRANCHING INSTRUCTIONS
CJNE A,direct,rel CJNE A,#data,rel CJNE Rn,#data,rel CJNE @Ri,#data,rel DJNZ Rn,rel DJNZ Rx,rel NOP Compares direct byte to the accumulator and jumps if not equal. Short jump. Compares immediate data to the accumulator and jumps if not equal. Short jump.
Compares immediate data to the register and jumps if not equal. Short jump.
Compares immediate data to indirect register and jumps if not equal. Short jump. Decrements register and jumps if not 0. Short jump. Decrements direct byte and jump if not 0. Short jump. No operation
DATA TRANSFER
MOV A,Rn MOV A,direct MOV A,@Ri MOV A,#data Moves the register to the accumulator Moves the direct byte to the accumulator Moves the indirect RAM to the accumulator Moves the immediate data to the accumulator
MOV Rn,A
Moves the accumulator to the register
MOV Rn,direct Moves the direct byte to the register MOV Rn,#data Moves the immediate data to the register MOV direct,A Moves the accumulator to the direct byte
DATA TRANSFER
MOV direct,A MOV direct,Rn MOV direct,@Ri MOV @Ri,A Moves the accumulator to the direct byte Moves the register to the direct byte Moves the indirect RAM to the direct byte Moves the accumulator to the indirect RAM MOV direct,direct Moves the direct byte to the direct byte MOV direct,#data Moves the immediate data to the direct byte
MOV @Ri,direct MOV @Ri,#data
MOVC A,@A+DPTR MOVC A,@A+PC
Moves the direct byte to the indirect RAM Moves the immediate data to the indirect RAM
Moves the code byte relative to the DPTR to the accumulator (address=A+DPTR)
MOV DPTR,#data Moves a 16-bit data to the data pointer
Moves the code byte relative to the PC to the accumulator (address=A+PC)
DATA TRANSFER
Moves the external RAM (8-bit address) to the accumulator Moves the external RAM (16-bit address) to the MOVX A,@DPTR accumulator Moves the accumulator to the external RAM (8-bit MOVX @Ri,A address) Moves the accumulator to the external RAM (16-bit MOVX @DPTR,A address) PUSH direct Pushes the direct byte onto the stack POP direct Pops the direct byte from the stack/td> XCH A,Rn Exchanges the register with the accumulator XCH A,direct Exchanges the direct byte with the accumulator XCH A,@Ri Exchanges the indirect RAM with the accumulator Exchanges the low-order nibble indirect RAM with the XCHD A,@Ri accumulator MOVX A,@Ri
LOGICAL INSTRUCTIONS
ANL A,Rn ANL A,direct ANL A,@Ri ANL A,#data ANL direct,A ANL direct,#data ORL A,Rn ORL A,direct ORL A,@Ri ORL direct,A ORL direct,#data AND register to accumulator AND direct byte to accumulator AND indirect RAM to accumulator AND immediate data to accumulator AND accumulator to direct byte AND immediae data to direct register OR register to accumulator OR direct byte to accumulator OR indirect RAM to accumulator OR accumulator to direct byte OR immediate data to direct byte
LOGICAL INSTRUCTIONS
XRL A,Rn XRL A,direct Exclusive OR register to accumulator Exclusive OR direct byte to accumulator
XRL A,@Ri
XRL A,#data XRL direct,A CLR A
Exclusive OR indirect RAM to accumulator
Exclusive OR immediate data to accumulator Exclusive OR accumulator to direct byte Clears the accumulator
XORL direct,#data Exclusive OR immediate data to direct byte
CPL A
SWAP A RL A RLC A RR A
Complements the accumulator (1=0, 0=1)
Swaps nibbles within the accumulator Rotates bits in the accumulator left Rotates bits in the accumulator left through carry Rotates bits in the accumulator right
RRC A
Rotates bits in the accumulator right through carry
BIT WISE INSTRUCTIONS
CLR C CLR bit SETB C SETB bit CPL C CPL bit ANL C,bit ANL C,/bit ORL C,bit Clears the carry flag Clears the direct bit Sets the carry flag Sets the direct bit Complements the carry flag Complements the direct bit AND direct bit to the carry flag AND complements of direct bit to the carry flag OR direct bit to the carry flag OR complements of direct bit to the carry flag Moves the direct bit to the carry flag Moves the carry flag to the direct bit
ORL C,/bit
MOV C,bit MOV bit,C
