Addressing mode of 8051
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The document discusses different addressing modes used by a CPU to access data. It describes 6 main addressing modes - direct, indirect, register, register specific, immediate, and external addressing. For each mode, it provides examples of instructions that use that mode to demonstrate how the CPU specifies the location and use of operands. It also distinguishes between using these modes to access internal memory locations like RAM versus external memory or Special Function Registers.
Addressing mode of 8051
- 1. Nitin Ahire XIE,Mahim Prof. Nitin Ahire 1
- 2. The CPU can access data various ways The data could be in a register, or memory or as an immediate value The various ways of accessing data are called addressing modes. Prof. Nitin Ahire 2
- 3. 1)Direct addressing mode 2)Indirect addressing mode 3)Register addressing 4)Register specific addressing (optional) 5)Immediate addressing 6)External Addressing ( Index ) a) Code access b) Data access Prof. Nitin Ahire 3
- 4. In this mode the operand is specified by an 8-bit address field In the instruction. One can access all the 128 bytes of internal RAM locations and each SFR. If the MSB bit = 0 then the location is within on chip internal RAM. If MSB bit = 1 then the location is SFR. Prof. Nitin Ahire 4
- 5. The location 00h to 7Fh to address the internal RAM . SFR addresses from 80h to FF h e.g. MOV A,40h MOV R0,14h Prof. Nitin Ahire 5
- 6. In this addressing mode, the instruction specifics a register which contains address of an operand i.e. the register hold the actual address that will be used in the data move operation. The R0 and R1 of each bank can be used as an index or pointer to memory location Prof. Nitin Ahire 6
- 7. The sign @ indicates the register acts as a pointer to memory locations E.g. MOV A,@ R1 Note : only register R0 and R1 can be used for indirect addressing mode . MOV A,@R2 invalid instruction. Prof. Nitin Ahire 7
- 8. Each bank consist of register R0 to R7 can be used as general purpose register for selection of bank register, the user has to modify the two bits of PSW These register can be used to stored the address or data in the register addressing mode Prof. Nitin Ahire 8
- 9. E.g. MOV R2,A MOV A, R1 MOV A,R7 Note: MOV R2,R7 is an invalid instruction Prof. Nitin Ahire 9
- 10. In this addressing mode the instruction refer to a specific registers such as accumulator or data pointer Example: DA A SWAP A Prof. Nitin Ahire 10
- 11. This method is the simplest method to get the data. In this addressing mode the source operand is a constant rather then a variable. As the data source is a part of instruction The # sign indicates that the data followed is immediate operand. Prof. Nitin Ahire 11
- 12. E.g. MOV A,#30h MOV P1,#0FF MOV DPTR, #1234h Prof. Nitin Ahire 12
- 13. (a) Code access (ROM access) Using these instructions only program memory can be accessed. This addressing mode is preferred for reading look up tables in the program memory. Either DPTR or PC can be used as pointer. Prof. Nitin Ahire 13
- 14. E.g. MOVC A,@A+DPTR MOVC A,@A+PC Prof. Nitin Ahire 14
- 15. (b) Data access (RAM access) Using this addressing mode the programmer can access the external Data memory E.g. MOVX A,@DPTR MOVX @R0,A Prof. Nitin Ahire 15