Register & Direct Addressing Mode – 8051

• Register Addressing: Operand in R0-R7, A, B. Encoding selects register via 3-bit field within opcode, e.g., INC R3, ADD A,R2, MOV A,R5 – fast, 1 byte.
• Direct Addressing: 8-bit direct address follows opcode, accesses internal RAM 00-7FH or SFR 80-FFH directly, e.g., MOV A,30H load from RAM location 30H, MOV 30H,A, MOV P1,80H. Note: Direct accesses SFR when 80-FFH range; via indirect @R0 that accesses upper RAM not SFR. 2 bytes. Direct can also address bit as second byte.