The 89C51 Microcontroller:-
The 89c51 is best microcontroller for beginners it is a low power and high performance 8-bit microcontroller.The 89c51 have 4K bytes of flash programmable and erasable read only memory (PEROM) .The 89c51 is belong to Atmel's 8051 family but 89c51 is advanced form of 8051 .
Features of 89C51 Microcontroller :-
- 4K bytes of In-System Reprogrammable Flash memory
- Fully static Operation : 0Hz to 24MHz
- 128 x 8-bit internal RAM
- 32 programmable I/O Pins
- Two 16-bit Times/Counters ( Timer 0 ,Timer 1 )
- One programmable Serial port
- Six interrupt sources
- Operating voltage = 5V
Pin configuration of 89C51 Microcontroller :-
The above figure shows the Pin configration of 89c51 Microcontroller , As shown from figure the 89c51 Microcontroller contains Four I/O ports three ports are multi function ports ( Port0 , Port1 and Port 3 ) but Port 1 is single function port .All Ports are 8-bit ports and upon rest all ports are consider as input .
PORT 0 :
The Port 0 can be used as input or output , the Port 0 is open drain port due this face each pin must be connected to 10K ohm pull up resistor . The Port 0 dual functional (AD0-AD7) Port mean when we connect the 89c51 Microcontroller to an external memory the Port 0 provides both address and Data .
PORT 1 :
The Port 1 can be used as input or output , this Port can not need any pull up resistors it had already pull up resistors internally .Port 1 is single functional Port .
PORT 2 :
The Port 2 can be used as input or output , just like Port 1 , Port 2 can not need any pull up resistors it had already pull up resistors internally . Port 2 is dual functional (A8-A15) Port , mean it provides upper 8-bit address to external memory (upper byte) .In simple words Port 0 and Port 2 provides the 16-bit address to external memory , when external memory is present .
PORT 3 :
Port 3 is very important port just like other three ports the Port 2 can be used as input or output and also no need any pull up resistor . Port 3 is also a Dual functional any very important functions Port .
Reset Pin :
The Reset Pin is active high pin , we will use two circuits for system reset one is manual reset and other is power on reset .
1: Manual Reset
2 : Power On Reset
Crystal Oscillator :
To make the 89C51 Microcontroller functional we need to connect the Crystal oscillator to pin 18 and 19 . Most commonly used crystal oscillators are 12 MHz and 11.0592 MHz .
VCC and GND :
The pin 40 is the VCC ( need to connect with +5V ) and pin 20 is Ground pin ( need to connect with 0V or negative terminal of battery or charger) .
EA/VPP , ALE/Prog and PSEN :
Pin 31 , EA ( External Access Enable ) this pin is normally connected to Vcc but when we connect this pin to GND the Microcontroller execute External ROM program(code).
VPP( Programming enable Voltage ) is normally connected to +5V .
Pin 30 ALE (Address Latch Enable ) is used for demultiplexing the address and data bus ALE pin is used when external memory is connected .
Pin 29 PSEN ( Program store Enable ) this pin provides an output signal that enables external program code( memory ) , this Pin is used when external memory is connected .
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