Notes: 8051 Microcontroller

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The 8051 microcontroller is one of the most popular general-purpose microcontrollers in use. They can be easily programmed using 8051 assembly language. This presentation includes all informative notes/tutorial on 8051 microcontroller. Various features of 8051 microcontroller are:

  • 8-bit CPU
  • 16-bit Program Counter
  • 8-bit Processor Status Word (PSW)
  • 8-bit Stack Pointer
  • Internal RAM of 128bytes
  • Special Function Registers (SFRs) of 128 bytes
  • 32 I/O pins arranged as four 8-bit ports (P0 – P3)
  • Two 16-bit timer/counters : T0 and T1
  • Two external and three internal vectored interrupts
  • One full duplex serial I/O

Intel’s original MCS-51 family was developed using N-type metal-oxide-semiconductor. The family was continued in 1996 with the enhanced 8-bit MCS-151 and the 8/16/32-bit MCS-251 family of binary compatible microcontrollers.

8051 Microcontroller Notes from MURTHY Y.N

One feature of the 8051 core is the inclusion of a boolean processing engine which allows bit-level boolean logic operations to be carried out directly and efficiently on select internal registers, ports and select RAM locations. This feature helped cement the 8051’s popularity in industrial control applications because it reduced code size by as much as 30%. Another feature is the inclusion of four bank selectable working register sets which greatly reduce the amount of time required to complete an interrupt service routine. With one instruction, the 8051 can switch register banks versus the time consuming task of transferring the critical registers to the stack, or designated RAM locations. These registers also allowed the 8051 to quickly perform a context switch.

Once a UART, and a timer if necessary, has been configured, the programmer needs only write a simple interrupt routine to refill the send shift register whenever the last bit is shifted out by the UART and/or empty the full receive shift register (copy the data somewhere else). The main program then performs serial reads and writes simply by reading and writing 8-bit data to stacks.


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