Page 70 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

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 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).

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CITS : E & H - Electronics Mechanic - Lesson 34 - 42