Functional Pin Diagram of 8051

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Pin diagram :

Micrcontroller 8051 is available in different packages in market DIP (Dual Inline Package),QFP (Quad Flat Package), TQFP (Thin Quad Flat Package), PQFP (Plastic Quad Flat Package) etc. Among them DIP package is mostly used. For explaining the pin diagram, we used here  40 pin DIP package. Pin configuration in detail is as given below :

Pin-40 : We use this pin for power source Vcc . Usually its +5V DC. 

Pins-32-39: We call this pin collectively Port 0 (P0.0 to P0.7) – It can be used as an I/O port as well as lower order address and data bus signals are multiplexed with this port  for external memory interfacing. It  is a only one bi directional I/O port in microcontroller 8051, it requires  external pull up resistors  to function this port as I/O port.

Pin-31: We call this pin as 'ALE' i.e. Address Latch Enable which is used to demultiplex the address and data signal of port 0 while external memory interfacing. Two ALE pulses are required for each machine cycle.

Pin-30: This pin we call  EA/ External Access which  is used to enable or disable external memory interfacing. If there is no additional external memory requirement, we put this pin in high state by connecting pin to Vcc.This is an active low pin.

Pin- 29:  We call this pin PSEN or Program Store Enable which is  used to read code from external program memory. This is an active pin.

Pins-21-28: We call this pin collectively Port 2 (P 2.0 to P 2.7)  which is used for  I/O purposes as well as  higher order address bus signals are multiplexed with this  port. This is a quasi bi directional port.

Pin- 20: We call this pin as a 'Vss'  we connect  ground (0 V) connection to this pin.

Pins- 18-19: We use these pins for  connecting an external crystal to create oscillation using on chip oscillator which is used as a clock source for 8051.

Pins- 10-17: We call this pin collectively Port 3. This port used for I/O purposes as well as it  serves some additional functions like  serial communication signals RxD and TxD, control signals for external memory interfacing RD and WR , interrupts, timer input etc. This is a quasi bi directional port with internal pull up.

Pin- 9: This pin we call as a RESET pin which is used to set the 8051 microcontroller to its initial state i.e. to reset the microcontroller.  If we want to reset the controller, the RESET pin must be set high for 2 machine cycles.

Pins- 1-8:We call this pin collectively Port 1. It is used for I/O purposes. Port 1 is an internally pulled up, quasi bi directional I/O port.






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