8051 Microcontroller Pin Diagram and Pin Description

 

8051 Microcontroller Pin Diagram and Pin Description

The document summarizes the key features and pin functions of the 8051 microcontroller. It has 40 pins total, with 32 pins used as I/O across four 8-bit ports (P0, P1, P2, P3). Many pins have multiple functions, such as serving as address lines when accessing external memory but as port pins otherwise. The remaining pins include power (VCC, GND) and oscillator (XTAL1, XTAL2) connections as well as pins for reset (RST), program store enable (PSEN), address latch enable (ALE), and external access (EA).

• Pins 1 to 8 − These pins are known as Port 1. This port doesnt serve any other functions. It is internally pulled up, bi-directional I/O port.

• Pin 9 − It is a RESET pin, which is used to reset the microcontroller to its initial values.

• Pins 10 to 17 − These pins are known as Port 3. This port serves some functions like interrupts, timer input, control signals, serial communication signals RxD and TxD, etc.

• Pins 18 & 19 − These pins are used for interfacing an external crystal to get the system clock.

• Pin 20 − This pin provides the power supply to the circuit.

• Pins 21 to 28 − These pins are known as Port 2. It serves as I/O port. Higher order address bus signals are also multiplexed using this port.

• Pin 29 − This is PSEN pin which stands for Program Store Enable. It is used to read a signal from the external program memory.

• Pin 30 − This is EA pin which stands for External Access input. It is used to enable/disable the external memory interfacing.

• Pin 31 − This is ALE pin which stands for Address Latch Enable. It is used to demultiplex the address-data signal of port.

• Pins 32 to 39 − These pins are known as Port 0. It serves as I/O port. Lower order address and data bus signals are multiplexed using this port.

• Pin 40 − This pin is used to provide power supply to the circuit.

8051 microcontrollers have 4 I/O ports each of 8-bit, which can be configured as input or output. Hence, total 32 input/output pins allow the microcontroller to be connected with the peripheral devices. 

Input Configuration 

If any pin of this port is configured as an input, then it acts as if it “floats”, i.e. the input has unlimited input resistance and in-determined potential.

Output Configuration 

When the pin is configured as an output, then it acts as an “open drain”. By applying logic 0 to a port bit, the appropriate pin will be connected to ground (0V), and applying logic 1, the external output will keep on “floating”. In order to apply logic 1 (5V) on this output pin, it is necessary to build an external pullup resistor.

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