Pin configuration of 8051 Microcontroller

8051 microcontroller is 40 pin dual in package (DIP) Ic chip. The 40 pins of 8051 microcontroller are configured as follows

*The input output pins are 32

*Control pins are three

*Oscillator input pins are 2

*2 Pins are power supply pin and ground pin

*1 Reset pin.

I/O Pins:

The input/output pins are provided in microcontroller are 32 pins. These pins are divided into four 8-bit parallel ports Po,P1,P2,P3. Among 32 pins 24 pins are designed to perform alternate functions.

Port-0 (pin 39-32):

The port-0 consists of 8 pins these are 8 bit input/output port. The pins Po.0 to Po.7 represents low order address ADo-AD7 of the two byte address ADo- AD15 of external memory is time multiplexed with the data being read or write. The port-o pins can be used to transfer data bytes between 8051 and external devices.

Port-1 ( pins 1-8 ):

The port one consists of 8 pins which are configured to perform only input/output function.

Port-2 ( pins 21-28 ):

The port two consists of 8pins form a parallel input function, it can configure high order address line (AD8-AD15) of a external memory address of two byte.

Port-3 ( pins 10-17 ):

This port consists of 8pins which perform bidirectional input/output. The alternate functions of port-3 are listed below.

P3.0 – RXD -> Receiving serial data

P3.1 – TXD -> Transmitting serial data

P3.2 – INTo -> Used for external interrupt O

P3.3 - INT1 -> Used for external interrupt 1

P3.4 – To. -> external time - 0 input

P3.5 - T1. -> external time - 1 input

P3.6 – WR -> Used to write the external data memory signal

P3.7 – RD -> Used to read the external data memory signal.

Pin- 40 & 20:

Pin 40 is a power supply pin provided with +5V of DC. Pin 20 is a ground pin used to eliminate shocking incidents.

Pin- 18 & 19:

The output of external clock generator is connected to pins 18 and 19, which must be connected to ground. In case if internal clock generator ( XTAL1 ), pin 19 connected to inverting amplifier input in oscillator circuit, (XTAL2) pin18 connected to output of inverting amplifier.

Pin-29 ( PSEN-Program Storage Enable ):

PSEN is an active, low output control signal which serve as read strobe to the external program memory. When microcontroller reads external program memory PSEN signal gets activated at every six oscillator periods.

Pin-30 (ALE-Address Latch Enable):

ALE is an active high output signal which is used to latch the lower byte of address.

Pin-31 (EA-External Access):

EA is an active low signal when EA is high, 8051 fetches program instructions from internal program memory for address 0000H to 0FFFH, when EA is low, 8051 fetches program Instructions from external memory for address 0000H to FFFFH.

Pin-9 (RESET):

RST pin can reset the microcontroller when a high signal should be applied to this pin for two machine cycles, while the oscillator is running.