Tuesday, July 2, 2013

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.

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