8051 Microcontroller

Major Features 

1. An 8 bit ALU 
2. 4 k x 8 ROM (or EPROM) 
3. 128 x 8 RAM 
4. Dual 16 bit timer event counter 
5. 32 I/O lines (Four 8-bit I/0 ports) 
6. Addresses 64 k bytes of program memory 
7. Full - featured serial port 

Architectural Block Diagram 

The 8051 microcontroller uses 32 pins for its four 8-bit input/output ports, and eight more pins for power, connecting to a clock crystal, and providing timing and control signals. The core components of the microprocessor, like the ALU, accumulator, stack pointer, and a set of general-purpose registers, are all connected to an internal 8-bit data bus. Each I/O port is linked to the internal data bus through registers that store data during I/O operations and control the ports. Additionally, the microcontroller has built-in ROM and RAM for storage and processing. 

8051 Memory Register Map 

The 8051 microcontroller addresses two memory spaces: program memory and data memory. Program memory is read-only, storing instructions that can be fetched but not written to or modified by the processor. The internal ROM is part of this space. Data memory, where internal RAM resides, is read-write, allowing the processor to store and manipulate data, but not execute instructions. The 8051 has 128 bytes of internal RAM for general storage and 22 special function registers outside this RAM. Program memory can be expanded from 4KB to 64KB, and external RAM up to 64KB can be added. In some cases, the 8051 can use combined memory for program and data storage, enabling downloaded programs to be executed directly from memory.