8051 Rotate Instructions

ROTATE INSTRUCTIONS

These instruction rotate the accumulator left, or right with or without carry. The instructions are RR, RRC, RL, RLC.

The RL instruction rotates accumulator left one bit left

Figure shows how the bits rotate left internally and then bit-7 to bit-0

No flags are affected by this instruction

Figure 7.1 : Rotate left logic operation

format	Example/ Operation	Opcode/ Encoding	Next Opcode Byte	Flags affected	Byte	Cycles
RL A	RL A An+1=An for n=0 to 7 A0=A7	00100011	—	none	1	1

Rotate the accumulator left one bit through carry

carry-bit into bit-0, and Bit-7 into carry

carry flag is update with bit-7

No other flags are affected by this operation.

format	example / Operation	Opcode/ Encoding	Subsequent Byte of Opcode	Flags affected	Cycles
RLC A	RLC A An+1=An for n=0 to 7 A0=C C=A7	00110011	—	C, P	1

RR Instruction rotate the accumulator Right one bit

Bit-7 to bit-6…..bit-1 to bit-0; bit -0 into bit-7

No flags are affected by this instruction.

Format	example /Operation	Opcode/ Encoding	Next byte of opcode	Flags affected	Cycles
RR A	RR A An = An+1 for n=0 to 7 A7 = A0	00000011	—	none	1

RRC is used to rotate accumulator through carry

Carry ->Bit-7, bit-7 to bit-6 and so on, and finally bit-0 in to carry.

No other flags are affected by this instruction.

Format	Example/ Operation	Opcode/ Encoding	Next Opcode Byte	Flags affected	Cycles
RRC A	RRC A An = An+1 for n=0 to 7 A7 = C C=A0	00010011	—	C,P	1

NOP instruction does nothing.
No registers or flags are affected on execution
It is typically used to generate a delay in execution or to reserve space in code memory

Format	Example Operation	Opcode/ Encoding	Flags affected	Byte	Cycles
NOP	NOP PC=PC+1	00000000	none	1	11