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CCS program syntax question

 
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ebarnes



Joined: 16 Apr 2007
Posts: 11

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CCS program syntax question
PostPosted: Mon Apr 14, 2008 9:54 am     Reply with quote
In the file LM75CIM3.c provided with the compliler there is a line i dont understand

It is " data=(signed long)datah*10; "

Why use the "Signed long" in parentheses here? the function is this
Code:
signed long read_full_temp() {
   signed long datah, datal;
   signed long data;

   i2c_start();
   i2c_write(0x90);
   i2c_write(0x00);
   i2c_start();
   i2c_write(0x91);
   datah=i2c_read();
   datal=i2c_read(0);
   i2c_stop();

   data=(signed long)datah*10;

   if(bit_test(datal,7))
   {
      if(data < 0)
      {
          data -= 5;
      }
      else
      {
         data += 5;
      }
   }

   data=(data)*90;
   data=(data/50)+320;

   return(data);
}
pmuldoon



Joined: 26 Sep 2003
Posts: 218
Location: Northern Indiana

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PostPosted: Mon Apr 14, 2008 10:57 am     Reply with quote
Here's a guess:

perhaps since i2c_read() returns an 8-bit int, the code was originally written with datah and datal being 8-bit integers. Then they were changed to unsigned longs and the casting was no longer needed, but never removed.
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