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Table of contents
1.
Introduction
2.
What is 8051 Microcontroller Pin Diagram?
3.
Description of the pins
3.1.
Pins 1 to 8
3.2.
Pin 9
3.3.
Pins 10 to 17
3.4.
Pins 18 and 19
3.5.
Pin 20
3.6.
Pins- 21-28
3.7.
Pin 29
3.8.
Pin 30
3.9.
Pin 31
3.10.
Pins 32 to 39
3.11.
Pin 40 (VCC) 
4.
Uses of pin diagram of the 8051 microcontroller
5.
Issues in Pin Diagram of the 8051 Microcontroller :
6.
Frequently Asked Questions
6.1.
How many pins are there in an 8051 microcontroller?
6.2.
Which pin of 8051 is used for Reset?
6.3.
Which of the given pins of 8051 is activated?
6.4.
What are the input pins in 8051 microcontroller?
7.
Conclusion
Last Updated: Mar 27, 2024
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8051 Microcontroller Pin Diagram

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Introduction

Hello Ninja, In this article, we will learn 8051 Microcontroller pin diagram, we’ll know about various pins, ports, etc.

8051 Microcontroller Pin Diagram

Let's look into Microcontroller before knowing about the 8051 Microcontroller Pin Diagram.

What is 8051 Microcontroller Pin Diagram?

8051 Microcontroller have been offered in some packages, including the 40-pin dual in-line package (dual-row pin integrated circuit package), 44-lead Plastic Leaded Chip Carrier, and thin quad flat pack. An 8051 microcontroller's pin orientation may change depending on the package, but the pin configuration remains the same.

8051 microcontroller pin diagram

Several packages are available for the 8051 microcontroller family (89C51, 8751, DS89C4xO, and 89C52), including quad-flat, leadless chip carrier, and dual-in-line (dual-row pin integrated circuit package). Each package has 40 pins used for various purposes, including I/O, address, Read and Write data, and interrupts. 
However, by lowering the number of I/O ports, some vendors offer a 20-pin version of the microcontrollers for much less demanding applications. However, the 40-pin chip is utilized by the vast majority of developers.

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Description of the pins

The 8051 microcontroller pin diagram is comprised of 40 pins, as may be seen below. Four Ports named P0, P1, P2, and P3 are used to store a total of 32 pins. Where each port has eight pins. The pin diagram and description for the microcontroller 8051 are therefore provided in this article.

Pins 1 to 8

It is also known as PORT 1. The 8-bit bidirectional input and output ports with inbuilt pull-up resistors make up PORT 1 Pins. Older 8051 microcontrollers only have an 8-bit I/O port on port 1. This port doesn't serve any additional purposes, unlike other ports.

Pin 9

It is an active HIGH pin, meaning the microcontroller will be reset if the RST Pin (Pin 9) is HIGH for at least two machine cycles. So it is the RESET pin used to reset it to its default values when operating or at the beginning of an application. 

Pins 10 to 17

It is also known as PORT 3. Interrupts, timer input, control signals, serial communication signals Receive Data (RxD) and Transmit Data (TxD), and other operations are served by this port.

  • Pin 3.0 - This pin is known as the serial input pin and its function is to receive data during serial communication.
     
  • Pin 3.1 - This pin is known as the serial output pin and its function is to transmit data during serial communication.
     
  • Pin 3.2 - This pin is used as an external trigger for interrupt 0.
     
  • Pin 3.3 - This pin is used as an external trigger for interrupt 1.
     
  • Pin 3.4 - This pin is for external input for Timer 0.
     
  • Pin 3.5 - This pin is for external input for Timer 1.
     
  • Pin 3.6 - This pin is used for writing data to the external memory.
     
  • Pin 3.7 - This pin is used for reading data from the external memory.
     

Pins 18 and 19

The pins connecting an external oscillator are 18 and 19, or XTAL 2 and XTAL 1, respectively. A Quartz Crystal Oscillator is often attached here.

Pin 20

The ground pin on an 8051 microcontroller is pin 20, or GND. It connects to the power supply's negative terminal (0V), representing 0V.

Pins- 21-28

The PORT 2 Pins on the 8051 Microcontroller are Pins 21 through 28. The PORT 2 pins function as either inputs or outputs because it is a bidirectional port. Additionally, PORT 2 pins work as the higher-order address byte when external memory is interfaced.

Pin 29

Program Store Enable, often known as PSEN, is used to interpret signals from external program memory.

Pin 30

This pin is linked to Vcc(Voltage Common Collector) to drag it high if there is no requirement for external memory.

Pin 31

It is also known as Address Latch Enable or ALE and is used to demultiplex the port 0 address data indication (for external memory interfacing). 

Pins 32 to 39

Pins 32 to 39 are known as Port 0 (P0.0 to P0.7), and they are multiplexed with low-order data/address bus signals to act as input/output ports (to provide the use of outer memory interfacing). 

Pin 40 (VCC) 

The circuit receives power supply voltage, or +5 Volts, from this pin, VCC (Voltage Common Collector).

 

The pin diagram of the 8051 microcontroller is as follows:

  1. VCC - This pin provides +5V power supply to the circuit.
     
  2. GND - This pin in connected to the negative terminal of the device to provide 0V supply.
     
  3. XTAL1 and XTAL2 - These pins are connected to the external oscillator to provide clock frequency.
     
  4. Reset - This pin is used to reset the microcontroller.
     
  5. Port 1 - This port is a collection of 8 bidirectional pins used for simple input/output operations. These do not serve any additional purpose.
     
  6. Port 2 - This port is a collection of 8 bidirectional pins used for simple input/output operations. These do not serve any additional purpose.
     
  7. Port 3 - This is a collection of 8 bidirectional pins.These act as higher-order address bytes whenever an additional external memory is interfaced with the 8051 microcontroller.
     
  8. Port 4 - This port is a collection of 8 bidirectional pins. These pins are used to provide functionality like Interrupts, Timer input, control signals and serial communication.
     
  9. INT0 - This pin is used as a trigger to external interrupt 0.
     
  10. INT1 - This pin is used as a trigger for external interrupt 1.
     
  11. T0 - This pin is used as external Timer 0.
     
  12. T1 - This pin is used as external Timer 1.
     
  13. WR - This pin gives the write signal for external memory.
     
  14. RD - This pin giver the read signal for external memory.
     
  15. ALE - This pin gives the signal to enable the latch to get the address for the external memory. 
     
  16. PSEN - This pin is used to give the signal for accessing the program memory.
     
  17. 17-24. Address bus - These pins transmit address from the microcontroller to the external memory.
     
  18. 25-32. Data bus - These pins transmit data from the microcontroller to the internal memory.
     
  19. RST - This pins gives the signal that the microcontroller is being reset.
     
  20. EA - This pin is used for selecting the program memory.
     
  21. VPP - This pin is used in programming and configuration of the microcontroller.
     
  22. 36-39. XTAL - These pins are connected to the oscillator to provide clock frequency.
     
  23. P1.0 (AD0) – P1.7 (AD7) - These pins are used to interface external devices with the microcontroller.

Uses of pin diagram of the 8051 microcontroller

The pin diagram of 8051 serves many uses in embedded systems. Some of the main uses of pin diagram include:

  • Pin identification - The pin diagram helps in identifying specific pins on the microcontroller. Each of these pins are labeled. This helps in easy identification of the pins.
     
  • Hardware Connections - The pin diagram helps in making physical connections between the microcontroller and external devices. These devices may include sensors, displays, memory devices etc.
     
  • Debugging and Troubleshooting - The pin diagram is useful for troubleshooting devices. With the help of pin diagram, we can compare the expected connections and signals on the pin diagram with the actual connections and identify the potential issues.
     
  • Memory Expansion - The pin diagram helps in expanding the storage of a microcontroller. We can add additional memory to the microcontroller by interfacing external RAM and ROM to the microcontroller.


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Issues in Pin Diagram of the 8051 Microcontroller :

The pin diagram of the 8051 microcontroller is standardized and well-defined. There are some issues associated with certain versions or derivatives of the 8051 microcontroller. There are several issues in the pin diagram of the 8051 microcontroller:

  • Pin compatibility: Some of the microcontrollers may have additional pins or slightly different pin configurations. This can cause compatibility issues when using different versions from different manufacturers.
     
  • Alternate pin functions: There are many cases where certain pins of the 8051 microcontroller can have multiple alternate functions. These functions can be interrupt inputs, UART pins, or timer/counter inputs. These alternate functions to specific pins may vary between different 8051 derivatives, leading to confusion during hardware design and programming.
     
  • Incomplete or incorrect documentation: Documentation for some 8051 microcontrollers may be incomplete or contain errors regarding pin functions or electrical characteristics. This can create challenges for developers trying to use specific pins for custom applications.
     
  • Pin voltage levels: The voltage levels supported by the I/O pins (high-level voltage and low-level voltage) can differ between various 8051 microcontrollers. This can impact the compatibility of the microcontroller with other components in a system.
     
  • Pinout variations: Some 8051 derivatives come in different package types with varying pinouts. If you are working with different package versions of the same microcontroller, you need to be aware of the pinout variations to ensure proper connections and functionality.

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Frequently Asked Questions

How many pins are there in an 8051 microcontroller?

The 8051 microcontroller has a 40-pin dual in-line package (DIP). These pins are used for power supply, crystal oscillator, reset, input/output ports, serial communication, timers/counters, interrupt, and program memory. However, some variants of the 8051 may have different pin configurations.

Which pin of 8051 is used for Reset?

The Reset pin denoted as the “RST” or “RESET” an usually labelled as pin 9 is used to reset the microcontroller. When the RESET pin is high for at least two machine cycles the microcontroller is set the instruction to reset.

Which of the given pins of 8051 is activated?

The pins which are triggered in logic high state are called active high or activated pins. Some of the most common activated pins include the Port 0, Port 1, Port 2, Port 3, XTAL1, XTAL2 etc.

What are the input pins in 8051 microcontroller?

The 8051 microcontroller has four input pins. These pins are also known as port input pins or general-purpose I/O (GPIO) pins. These pins are programmable and can be configured to function as input or output pins based on the needs of the application.

Conclusion

In this article, we discussed the 8051 Microcontroller Pin Diagram. We hope our blog on the 8051 microcontroller pin diagram was helpful.

To better understand topics like the 8051 Microcontroller Pin Diagram, check the articles below.

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