Microcontroller8051

Pin Description of the 8051

123

4567891011121314151617181920

403938

3736353433323130292827262524232221

P1.0P1.1P1.2

P1.3P1.4P1.5P1.6P1.7RST

(RXD)P3.0(TXD)P3.1

(T0)P3.4(T1)P3.5

XTAL2XTAL1

GND

(INT0)P3.2

(INT1)P3.3

(RD)P3.7(WR)P3.6

VccP0.0(AD0)P0.1(AD1)

P0.2(AD2)P0.3(AD3)P0.4(AD4)P0.5(AD5)P0.6(AD6)P0.7(AD7)

EA/VPPALE/PROG

PSENP2.7(A15)P2.6(A14)P2.5(A13)P2.4(A12)P2.3(A11)P2.2(A10)P2.1(A9)P2.0(A8)

8051

(8031)

Pin Description

• Pin 1-8(port 1,p1.0 to p1.7): These are 8 pins of port 1. Each of these pins can be configured as input or output.

• Pin 9(Reset): A positive voltage pulse on this pin resets the microcontroller.

• Pin 10-17(Port3, P3.3 to P3.7): these are dual function pins. Similar to port 1, each of these pins can serve as universal input or output.

• Pin 18,19 (X1 ,X2): These are the input and

output pins of internal oscillator. A quartz crystal isusually connected to these pins.

• These 2 pins provide external clock.• Way 1：using a quartz crystal oscillator• Way 2：using a TTL oscillator

• Pin 20(GND): Ground

• Pin 21-28(Port2,P2.0 to P2.7): If there is nointention to use external memory then these portpins are configured as universal input/output. Incase external memory is used then the higheraddress byte ie address A8-A15 will appear on thisport.

Pins of 8051（1/4）

• Vcc（pin 40）：• Vcc provides supply voltage to the chip.

• The voltage source is +5V.

• Pin 12(INT0): Interrupt 0 input• Pin 13(INT1): Interrupt 1 input

• Pin 13(T0): Counter 0 clock input• Pin 14(T1): Counter 1 clock input

• Pin 15(WR): Signal for writing to externaladditional RAM

• Pin 16(RD): Signal for reading from external Ram.

Pins of 8051（3/4）

• /EA（pin 31)

• By applying logic 0 to this pin ,P2 and P3 areused for data and address transmission with noregards to whether there is internal memory ornot. Otherwise by applying logic 1bto EA pin,the microcontroller will use both memories, firstinternal and afterwards external (if exists) .

• PSEN（pin 29）：program store enable

• If external Rom is used for storing program thenit has logic 0 value every time themicrocontroller reads a byte from memory.

Pins of 8051

• ALE（pin 30）：address latch enable

• It is an output pin and is active high.

• This pin is used when multiple memory chips areconnected to the controller and only one of them needsto be selected.

Architecture of 8051