Instruction Set of 80C51

Arithmetic Instructions
The menu of arithmetic instructions is listed in Table 1.4.1 The table indicates the addressing modes that can be used with each instruction to access the operand.
For example, the ADD A, instruction can be written as:

ADD a, 7FH (direct addressing)
ADD A, @R0 (indirect addressing)
ADD a, R7 (register addressing)
ADD A, #127 (immediate constant)

The MUL AB instruction multiplies the Accumulator by the data in the B register and puts the 16-bit product into the concatenated B and Accumulator registers.

The DIV AB instruction divides the Accumulator by the data in the B register and leaves the 8-bit quotient in the Accumulator, and the 8-bit remainder in the B register.

Table 1.4.1. MCS-51 Arithmetic Instruction

Mnemonic	Operation	Addressing Mode				Exect.
		Dir	Ind	Reg	Imm	Timer uS
Add A,[byte]	A=A+[byte]	V	V	V	V	1
Addc A,[byte]	A=A+[byte]+C	V	V	V	V	1
Subb A,[byte]	A=A-[byte]-C	V	V	V	V	1
Inc A	A=A+1	Accumulator Only				1
Inc [byte]	[byte]=[byte]+1	V	V	V		1
Inc DPTR	DPTR=DPTR+1	Data Pointer Only				2
Dec A	A=A-1	Accumulator Only				1
Dec [byte]	[byte]=[byte]-1	V	V	V		1
Mul AB	B:A=BxA	Accumulator and B Only				4
Div AB	A=Int[A/B] B=Mod[A/B]	Accumulator and B only				4
DA A	Dec Adjust	Accumulator Only				1

Logical Instructions
Table 1.4.2 shows the list of 80C51 logical instructions. The instructions that perform Boolean operations (AND, OR, Exclusive OR, NOT) on bytes perform the operation on a bit-by-bit basis. That is, if the Accumulator contains 00110101B and byte contains 01010011B, then:

Table 1.4.2. MCS-51 Logical Instructions

Mnemonic	Operation	Addressing Mode				Exect.
		Dir	Ind	Reg	Imm	Timer uS
Anl A,[byte]	A=A and [byte]	V	V	V	V	1
Anl [byte],A	[byte]=[byte] anl A	V	V	V	V	1
Anl [byte],#data	[byte]=[byte] and#data	V	V	V	V	1
Orl A,[byte]	A=A or [byte]	Accumulator Only				1
Orl [byte] ,A	[byte]=[byte]orl A	V	V	V		1
Orl [byte],#data	[byte]=[byte] or #data	Data Pointer Only				2
Xrl A,[byte]	A=A xor [byte]	Accumulator Only				1
Xrl [byte],A	[byte]=[byte] xor A	V	V	V		1
Xrl [byte] ,#data	[byte]=[byte] xor#data	Accumulator and B Only				4
CLR A	A=00h	Accumulator only				1
CPL A	A= not A	Accumulator only				1
RL A	Rotate A left 1 bit	Accumulator only				1
RLC A	Rotate A left trough Carry	Accumulator only				1
RR A	Rotate A right 1 bit	Accumulator only				1
RRC	Rotate A right trough carry	Accumulator only				1
SWAP A	Swap nibbles in A	Accumulator only				1