8051 family members (e.g., 8751, 89C51, 89C52, DS89C4xO) come in different packages, such as DIP (dual in-line package), QFP (quad flat package), and LLC (leadless chip carrier),
They all have 40 pins that are dedicated to various functions such as I/O, RD, WR, address, data, and interrupts.However, since the vast majority of developers use the 40-pin chip.
Pins 1 – 8 (port 1):
- this all are Port 1.it doesn’t provide any other purpose.
- Port 1 is a domestically pulled up, quasi bi directional Input/output port.
Pin 9 (RESET):
- RESET pin is utilized to set the micro-controller 8051 to its primary values, whereas the micro-controller is functioning or at the early beginning of application.
- The RESET pin has to be set elevated for two machine rotations.
Pins 10 – 17(Port 3)
- This port also supplies a number of other functions such as timer input, interrupts, serial communication indicators TxD & RxD, control indicators for outside memory interfacing WR & RD, etc.
- This is a domestic pull up port with quasi bi directional port within.
Pins 18 and 19 (XTAL1 & XTAL2):
- These are employed for interfacing an outer crystal to give system clock.
Pin 20 (Vss)
- it symbolizes ground (0 V) association.
Pins- 21-28(Port 2):
- as Input/output port,
- senior order address bus indicators are multiplexed with this quasi bi directional port.
Pin- 29 (PSEN):
- Program Store Enable or PSEN is employed to interpret sign from outer program memory.
Pin-30 (EA):
- External Access or EA input is employed to permit or prohibit outer memory interfacing.
- If there is no outer memory need, this pin is dragged high by linking it to Vcc.
Pin-31 (ALE):
- It is brought into play to de-multiplex the address data indication of port 0 (for outer memory interfacing).
Pins 32-39 (Port 0)
- as Input/output port
- low order data & address bus signals are multiplexed with this port (to provide the use of outer memory interfacing).
- This pin is a bi directional Input/output port (the single one in microcontroller 8051) and outer pull up resistors are necessary to utilize this port as Input/output.
Pin-40 (Vcc)
- it is the chief power supply.
- By and large it is +5V DC.
