Features of 8051
The main features of 8051 microcontroller are:
i. RAM – 128 Bytes (Data memory)
ii. ROM – 4Kbytes (ROM signify the on – chip program space)
iii. Serial Port – Using UART makes it simpler to interface for serial communication.
iv. Two 16 bit Timer/ Counter
v. Input/output Pins – 4 Ports of 8 bits each on a single chip.
vi. 6 Interrupt Sources
vii. 8 – bit ALU (Arithmetic Logic Unit)
viii. Harvard Memory Architecture – It has 16 bit Address bus (each of RAM and ROM) and 8 bit Data Bus.
ix. 8051 can execute 1 million one-cycle instructions per second with a clock frequency of 12MHz.
This microcontroller is also called as “System on a chip” because it has all the features on a single chip. The Block Diagram of 8051 Microcontroller is as shown in Figure 1.1
Figure 1.1 Block Diagram of 8051 Microcontroller
The 4 discrete types of memory in 8051 are:
i. Internal RAM – This memory is located from address 0 to 0xff. The memory locations from 0x00 to 0x7F are accessed directly. The bytes from 0x20 to 0x2F are bit-addressable. Loading R0 and R1 the memory location from 0x80 to 0xFF can easily accessed.
ii. Special Function Registers (SFR) – Located from address 0x80 to 0xFF of the memory location. The same instructions used for lower half of Internal RAM can be used to access SFR’s. The SFR’s are bit addressable too.
iii. Program Memory – This is read only memory which is located at address 0. With the help of 16 bit Special Function Register DPTR, this memory can also save the tables of constants.
iv. External Data Memory – Located at address 0. The Instruction MOVX (Move External) should be used to access the external data memory.