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8051 Microcontroller Cheat Sheet

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A concise set of notes which is used mainly for quick reference is known as a cheat sheet or crib sheet. These sheets were used by many students to prepare/ revise for their exam/test. The cheat sheet provides you with very useful data regarding a subject and helps you remember. This article provides brief information on the 8051 microcontroller cheat sheet which includes the information about the microcontroller.

1. Introduction:

  • The 8051 microcontroller is an 8-bit microcontroller with Harvard architecture.
  • Developed by Intel in 1980, widely used in embedded systems.

2. Architecture:

CPU:

  • 8-bit ALU (Arithmetic Logic Unit).
  • 16-bit PC (Program Counter) and DPTR (Data Pointer).
  • 8-bit registers (Accumulator, B register, and more).

Memory:

  • 128 Bytes of RAM (Data memory).
  • 4 KB of ROM/EPROM (Program memory).
  • On-chip data memory and external code memory support.

Clock:

  • Typically operates at 12 MHz.
  • Two 16-bit timers/counters (Timer 0 and Timer 1).

3. Instruction Set:

  • Over 100 instructions, including data transfer, arithmetic, logical, and control operations.
  • Instructions vary in length (1 to 3 bytes).

4. Registers:

  • Accumulator (A): Primary register for arithmetic and logic operations.
  • B Register: Used in multiplication and division.
  • Data Pointer (DPTR): 16-bit pointer for external data memory.
  • Program Counter (PC): 16-bit register for program memory addressing.

5. Interrupts:

  • Supports external hardware interrupts (INT0, INT1) and internal interrupts (Timer, Serial).
  • Interrupt enable and disable instructions (EI, DI).

6. I/O Ports:

  • Four parallel I/O ports (P0, P1, P2, P3).
  • Bit-addressable and byte-addressable ports.
  • P0 and P2 have internal pull-ups.

7. Serial Communication:

  • UART for serial communication (TXD, RXD).
  • 8-bit data, variable baud rate.

8. Timers/Counters:

  • Two 16-bit timers (Timer 0 and Timer 1).
  • Mode 1: 16-bit mode with auto-reload.
  • Mode 2: 8-bit mode with auto-reload.

9. Memory Organization:

  • Program memory (Code space): Addresses 0000H to FFFFH.
  • Data memory (RAM): Addresses 00H to 7FH.
  • Special Function Registers (SFRs): Addresses 80H to FFH.

10. Instruction Set Examples:

The 8051 microcontroller has a rich set of instructions, covering a wide range of operations including data transfer, arithmetic and logic operations, control flow, and more. Here is a list of some common instructions for the 8051 microcontroller:

Data Transfer Instructions:

  • MOV A, source: Move data from source to accumulator.
  • MOV destination, source: Move data from source to destination.
  • MOVC A, @A+DPTR: Move code byte from address A+DPTR to accumulator.

Arithmetic Instructions:

  • ADD A, source: Add source to accumulator.
  • ADD A, #data: Add immediate data to accumulator.
  • ADDC A, source: Add source and carry flag to accumulator.
  • SUBB A, source: Subtract source and borrow from accumulator.
  • INC destination: Increment the value at the destination.

Logical Instructions:

  • ANL A, source: Bitwise AND source with accumulator.
  • ORL A, source: Bitwise OR source with accumulator.
  • XRL A, source: Bitwise XOR source with accumulator.
  • CJNE A, data, label: Compare A with immediate data, jump if not equal.

Control Flow Instructions:

  • JMP address: Jump unconditionally to the specified address.
  • JC/JB/JNB/JNC/JZ/JNZ, label: Jump based on carry, bit, zero, or non-zero condition.
  • CALL address: Call subroutine at the specified address.
  • RET/RETI: Return from subroutine or interrupt.

Register Move Instructions:

  • MOVX A, @DPTR: Move data from external RAM to accumulator.
  • MOVX @DPTR, A: Move data from accumulator to external RAM.

Bit Manipulation Instructions:

  • SETB bit: Set a specified bit.
  • CLR bit: Clear a specified bit.
  • CPL bit: Complement (invert) a specified bit.

Rotate and Swap Instructions:

  • RL A/RLC A: Rotate accumulator left with or without carry.
  • RR A/RRC A: Rotate accumulator right with or without carry.
  • SWAP A: Swap the nibbles in the accumulator.

Data Compare and Skip Instructions:

  • CJNE A, data, label: Compare A with immediate data, jump if not equal.
  • DJNZ destination, label: Decrement destination, jump if not zero.

Stack Operation Instructions:

  • PUSH source/POP destination: Push data onto or pop data from the stack.

Serial Communication Instructions:

  • MOV SBUF, A/MOV A, SBUF: Move data between accumulator and serial buffer.
  • MOV SCON, #data: Initialize serial communication control register.

External Memory Instructions:

  • MOVX A, @DPTR/MOVX @DPTR, A: Move data between accumulator and external RAM.

Miscellaneous Instructions:

  • NOP: No operation (used for timing purposes).
  • HALT: Halt the CPU until an interrupt occurs.

This is a subset of the 8051 instruction set. The actual instruction set may vary slightly depending on the specific variant of the 8051 microcontroller. 

  1. Special Function Registers (SFRs):
  • PCON: Power control register.
  • TCON: Timer control register.
  • SCON: Serial control register.
  • IP: Interrupt priority register.
  • IE: Interrupt enable register.
  1. Programming Tools:
  • Keil uVision, SDCC, and other compilers.
  • Flash programming tools for EPROM-based versions.

11. Special Function Registers (SFRs):

  • PCON: Power control register.
  • TCON: Timer control register.
  • SCON: Serial control register.
  • IP: Interrupt priority register.
  • IE: Interrupt enable register.

12. Programming Tools:

  • Keil uVision, SDCC, and other compilers.
  • Flash programming tools for EPROM-based versions.