8051 Memory Organization – A Comprehensive Guide
8051 Memory Organisation
The 8051 family of microcontrollers are built with a variety of internal memory options. The internal memory of 8051 is organized into four main sections: Program Memory, Data Memory, Special Function Registers, and Bit Addressable Memory. Together, all these memory elements form the 8051 memory organization.
Program Memory
The Program Memory of the 8051 stores the code for the processor to execute. This memory is often called ROM, which stands for Read-only Memory. It is non-volatile, meaning that the program stored in the memory will remain even when the power is removed. The size of the Program Memory can vary depending on the specific 8051 model. On most 8051 models, the Program Memory is sized between 4K and 64K bytes.
Data Memory
The 8051 Data Memory is divided into two distinct sections: Internal Data Memory and External Data Memory. The Internal Data Memory is used to store program instructions and data while the processor is running (i.e., while the code is being executed). This memory is volatile, meaning that when the power is removed, the contents of this memory will be lost. The size of the Internal Data Memory is typically 256 bytes. The External Data Memory is used for larger amounts of data storage and is typically used for storing variables and program data. The size of this memory is not fixed and can vary from 128 bytes to several megabytes, depending on the type of 8051.
Special Function Registers (SFRs)
The Special Function Registers of the 8051 contain control registers, status registers, and ports for communication with the outside world. These registers are used for control and status operations, as well as for I/O operations. Most 8051s have 16 SFRs, but some models may have more or fewer, depending on the design.
Bit Addressable Memory
The Bit Addressable Memory of the 8051 allows each bit of the 8-bit word to be accessed individually. This feature is useful for controlling individual pins of an output port, or for storing small numbers of flags or status bits.
