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This is my first question as I am new to coding.

Well, I am trying to use a MCP digipot in SPI. As I am using a PIC16, writing in C, I learned that the XC8 library couldn't be included in a PIC16 project... So I thought I would learn a lot doing it by bit banging, understanding what I do...

But...Doesn't seem to work ! So I have made a LED version with some delay in order to see what was happening.

I have two problems: First, the "command" data doesn't seem to be shifted. I can only see a flash for the first bit then it turns out. The "clock" led works fine, flashing 8 times.

Also, I don't understand why my infinite loop isn't infinite. I get a few cycles then the main function is called back and so on. It has something to do with my delays as it changes the number of cycles when I change the delay.

Here is my code:

#include <stdio.h>
#include <pic16f18875.h>

#define temoin LATAbits.LATA0
#define CS LATAbits.LATA1
#define CLK LATAbits.LATA2
#define DAT LATAbits.LATA3

#define MASK = 0x80 //isolate the MSB

unsigned char commande = 0b10011000; //led sequence to be observed (command)

void delay(void)
    {              int f, g;
                    for(f=0;f<1000;f++)
            {
                      for(g=0;g<1;g++)
                  {  } } }     //simple delay                    

void main()
{
        int i;

//init                        
        TRISA=0x00;    //porta as output
        LATA = 0x00; //init all bits to 0        

        CS=0;   //enable writing               

 //send command

        for (i=0; i<8; i++) //browse through the command byte
            {

            if (commande & MASK) //read msb and compare                      
                     DAT = 1;                        
            else                        
                     DAT = 0;


                CLK=1; //clock signal
                delay();                   
                CLK=0;
                delay();

              commande <<=1; //left shift, read next bit 

            }

        CS = 1;

        while (1) //just a heartbeat
        {
          temoin = 1;
          delay();             
          temoin = 0;
          delay();             
        }
}

I have really tried a lot to find any info on the web but none worked fine for me. I might just lack a special C language knowledge, but I couldn't tell what.

Thanks in advance !

Cheers

Ted Hook
  • 11
  • 1

1 Answers1

0

I'm pretty sure your problem is simply that your #define is messed up:

#define MASK = 0x80 //isolate the MSB
             ^- ???

That equal sign ends up getting treated as part of the definition, so the preprocessor will expand

if (commande & MASK) //read msb and compare

to:

if (commande & = 0x80) //read msb and compare

which isn't what you wanted at all! This ends up modifying commande in the if statement, masking out all of the bits lower than 0x80.

Removing the = in the definition should fix this.

With regard to the other part -- the infinite loop not being infinite -- make sure that your processor doesn't have a watchdog timer enabled. You may need to disable it in fuse bits.