[moved] Ds3231 RTC: temperature display (mikroC)

[zuisti]

On request I wrote a simple and fast function to display the temperature
measured by the Ds3231 internal sensor.

- no any floating operation (integer arithmetic only)
- no any character buffer (each digit is displayed immediately after computed)

From the Ds3231 datasheet:
Temperature is represented as a 10-bit code with a resolution of 0.25°C
and is accessible at location 11h and 12h. The temperature is encoded
in two’s complement format. The upper 8 bits, the integer portion, are
at location 11h and the lower 2 bits, the fractional portion, are in
the upper nibble at location 12h. For example, 00011001 01b = +25.25°C

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Code C - [expand]
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void Ds3231_Temp_CP(void) { // "-00.00", range: -99 to +127 degree
   // written by (©) zuisti (Istvan K)
   char msb, lsb, tmp;
 
   // read the two temperature registers:
   I2C1_start();
   I2C1_Wr(0xD0); // Ds3231_write address
   I2C1_Wr(0x11); // register address (temp msb, integer part), to be read first
   I2C1_Repeated_Start();
   I2C1_Wr(0xD1); // Ds3231_read address
   msb = I2C1_Rd(1); // w. ACK
   lsb = I2C1_Rd(0); // w. NACK (last read)
   I2C1_stop();
 
   tmp = ' ';
   if (msb.B7) { // SIGN_bit = 1: negative
      tmp = '-';
      // two's complement conversion:
      msb ^= 0xFF;
      if (!lsb)
         ++msb; // required if the fractional portion is zero
      else
         lsb.B0 = 1; // negative fract. sign, normally it is 0
   }
   else if (msb > 99) {
      msb -= 100;
      tmp = '1';
   }
   // the first char is a space, '-' or '1':
   Lcd_Chr_CP(tmp);
   
   // convert msb (binary value) to 2 ASCII digits
   for ( tmp = '0' ; msb > 9 ; ++tmp, msb -= 10 );
   // display integer portion:
   Lcd_Chr_CP(tmp);
   Lcd_Chr_CP(msb + '0'); // modulo 10 as ASCII digit
 
   // decimal point:
   Lcd_Chr_CP('.');
   
   // compute fract. part:
   msb = '0';
   tmp = '0';
   if (lsb) {
      // positive 7,6 bits: 01(25), 10(50), 11(75)
      // negative 7,6 bits: 01(75), 10(50), 11(25)
      if (!lsb.B6)
         msb = '5'; // 50
      else {
         msb = '2';
         tmp = '5';
         if (lsb.B0) // negative fract. (see above): 25 <> 75
            lsb.B7 = !lsb.B7;
         if (lsb.B7)
            msb = '7';
      }
   } // fract. part
   Lcd_Chr_CP(msb);
   Lcd_Chr_CP(tmp);
} // end of Ds3231_Temp_CP()
 
// ******** Usage (a possible example):
 
 Lcd_Out(1, 1, "Temp:");
 Ds3231_Temp_CP();
 Lcd_Chr_CP(0xDF); // dec 223 = degree sign
 Lcd_Chr_CP('C');

---

 

[KlausST]

Re: Ds3231 RTC: temperature display (mikroC)

Hi,

No question?

Klaus

 

[zuisti]

Re: Ds3231 RTC: temperature display (mikroC)

No question?

Yes, because my post above is a (well-functioning) solution, not a question. I just wanted to help others, so I published it.
Kind mods, please move this to the right place (I couldn't find any better). Thank you.
Regards:
zuisti

 

[KlausST]

Re: Ds3231 RTC: temperature display (mikroC)

Hi,

I´ll move it to the "Hardware and PCB Design" --> "Show your DIY" section

But are you usure it is helpful:
* without schematic
* without knowing about the display
* without knowing what microcontroller
* without knowing about compiler
and so on...

Klaus