Friday, September 3, 2010

PIC16F887/877 programming in C Tutorial 2 (S.S Display Interfacing)

Interfacing Seven Segment (c.c) Display

In this tutorial i will show you how to interface S.S display with PIC16F887/877. For this we required 74hc573 latches, 74hc238 decoder, and 74ls48 bcd2dec converter.

Latches are used to enable/disable the S.S, 74hc234 a 3x8 decoder selects the appropriate latch to be enable/disable. 74ls48 just converts the bcd input to respective decimal output to operate S.S properly. 

Now lets write a small program that display the digital manual input at S.S, enter by the user; by using 8-way dip switch.

void main() {

     int x,y,i,j;
     trisd=255;      //all bits for input

 ///////////////// comment 4 pic16f877/////////





Now come towards the code; portc is utilized for o/p, and manual i/p is applied at portd, here. As the ports are 8-bit so, maximum i/p would be 255(0-255); we have to display them on three S.S, for this we have to separate the digits of i/p. Modulus '%'  do this job; let say the i/p is 255, then first we have to display 5 then 5 and then 2; to do this we use x%10. Where x is an integer that has the manual i/p. Where modulus operator returns the remainder of integer division, so after this we have 5 stored in y (as 255%10 = 5, remainder is 5).

After getting the digit, it should be display on 3rd S.S; so to select this latch just or '|' y with proper integer, which in this case is 0 (as my 3rd S.S as attached to 0 o/p of latch, 2nd is to 1st and so on). So, after doing this we have 5 in 8-bit and latch 0 is selected. Now display it by assigning it to port.

To display 2nd digit first reduce the i/p by dividing it with 10; 255/10 gives 25, as we are storing this value in an integer; so x is equal to 25, now. J is incremented by 16 because we have to select the first latch (see the diagram for more detail).

In the same fashion, to display the first digit; select proper latch, divide and take modulus and display it, that is it. Here i is used to run this process for three times (means to display all the i/p digit on three S.S).

For reset circuitry  please refer to first tutorial.
connection diagram

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