There are four addressing modes in 8051.
(i) Immediate addressing mode: the data source is available immediately as a part of instruction itself. Example: MOV A, #8bit data
(ii) Register addressing mode: the source and destination register names are parts of the opcode in instruction. Example: MOV A, R0
(iii) Direct addressing mode: the source and/or destination may be the internal RAM locations. Example: MOV 90h, #50h
(iv) Indirect addressing mode: the source or destination address may be indicated the content of index register. Example: MOV @R1, #40h
