Understanding the Memory Organization of 8051 Microcontroller Programming

We know how commonly the 8051 Microcontroller is used in embedded system, nowadays. So, it will be a good idea to understand how memory is organized in 8051 Microcontroller. To start with, we see that organization of memory depends on two architecture types that are:

• Von Neumann architecture: The architecture also known as Von Neumann model or Princeton architecture comprises both, address as well as data memories, on a single unit.
• Harvard architecture: In this architectural type, both the memories, address and data, are treated as separate units.

8051 Microcontroller’s memory can be categorized into Program Memory and Data Memory, on the broad level. While, Program Memory is the ROM of 8051 Microcontroller; the Data Memory is RAM. Following is a brief description of the two memory types:

• Program Memory (ROM): This memory type saves the executed code of a program permanently. Default size of the memory on chip is 4K; however, depending on the requirement, you can add external memory upto 60K in size. Thus, total Program Memory available on 8051 Microcontroller is 64K in size. The transfer process of executed program from default to external memory is automatic in nature. You must also note that handling of external memory is decided by the logic state of EA (External Access) pin.

• Data Memory (RAM): This memory type stores the code of executed program temporarily. While, internal data RAM is 128 bytes in size; it can have external memory upto 64K in size. Thus, total Data Memory available on 8051 Microcontroller is 64K + 128 bytes in size. Further, internal Data Memory RAM is divided in three parts, namely, Register Banks, Bit Addressable Area, and Scratch Pad Area.

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