Making multiple input by 3 wire Interfacing .

Parallel to serial  Interfacing with Micro controller 

Interfacing with 74HC165 with 8051

   I am trying to make multiple input with using minimum input port of micro controller ,ie 3 wire .
By using a 3 wire we can interface more input as we wish.

 I am making a tutorial for it , Basics of 74HC165  which is a parallel to serial shift register .


Only three pin is connected with this IC . 
1)   SH/LD  or PL  is used load  parallel data to the IC .A low pulse (ground) is applied for store the         parallel data at the pin from A to H . And a High (5 Volt) is applied to stop the reading from the          PIN A to H .
2) Then to read the loaded or saved data to Micro controller we have to give clock to the PIN 2 of           74HC165  (CLK) . 8 pulses is applied to read 8 bit (Pin A to B)

3) QH / SO . serial out pin is used to get the stored parallel data to serially.

The CLK INH pin must be connect in ground for enable clock.

    To use cascaded 74HC165 for increasing i/p .connect the Seriall output pin (PIN 9) of first satge into serial input of first stage see the following circuit.

see the code below

#include "lcd.h"  
sbit PL  = P1^0;   // Loading parallel data to HC165.
sbit CLK = P1^1;   // Clock pulse to HC165.
sbit Beep  = P1^2;   // 
sbit data_in  = P1^3;

  void clock(void);
  void display(unsigned char value);
void main()
 unsigned char position ,no_of_ip = 17;
  string("   gElectron");     

      PL = 0 ;
  PL = 1;

   for(position = 1; no_of_ip > position; position++ , clock())
    if(data_in == 1)


 void clock(void)
   CLK = 1;
   CLK = 0;


void display(unsigned int value)
  unsigned int a[1];
    Beep =   1;
    string("Pressed key ");
     Beep = 0;

Download the whle file here github.

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