meas_to_cel.c

来自「Source code for driving RFM01 fm radio r」· C语言 代码 · 共 60 行

#include "./ds18x20.h"

/* 
   convert raw value from DS18x20 to Celsius
   input is: 
   - familycode fc (0x10/0x28 see header)
   - scratchpad-buffer
   output is:
   - cel full celsius
   - fractions of celsius in millicelsius*(10^-1)/625 (the 4 LS-Bits)
   - subzero =0 positiv / 1 negativ
   always returns  DS18X20_OK
   TODO invalid-values detection (but should be covered by CRC)
*/
uint8_t DS18X20_meas_to_cel( uint8_t fc, uint8_t *sp, 
	uint8_t* subzero, uint8_t* cel, uint8_t* cel_frac_bits)
{
	uint16_t meas;
	uint8_t  i;
	
	meas = sp[0];  // LSB
	meas |= ((uint16_t)sp[1])<<8; // MSB
	//meas = 0xff5e; meas = 0xfe6f;
	
	//  only work on 12bit-base
	if( fc == DS18S20_ID ) { // 9 -> 12 bit if 18S20
		/* Extended measurements for DS18S20 contributed by Carsten Foss */
		meas &= (uint16_t) 0xfffe;	// Discard LSB , needed for later extended precicion calc
		meas <<= 3;					// Convert to 12-bit , now degrees are in 1/16 degrees units
		meas += (16 - sp[6]) - 4;	// Add the compensation , and remember to subtract 0.25 degree (4/16)
	}
	
	// check for negative 
	if ( meas & 0x8000 )  {
		*subzero=1;      // mark negative
		meas ^= 0xffff;  // convert to positive => (twos complement)++
		meas++;
	}
	else *subzero=0;
	
	// clear undefined bits for B != 12bit
	if ( fc == DS18B20_ID ) { // check resolution 18B20
		i = sp[DS18B20_CONF_REG];
		if ( (i & DS18B20_12_BIT) == DS18B20_12_BIT ) ;
		else if ( (i & DS18B20_11_BIT) == DS18B20_11_BIT ) 
			meas &= ~(DS18B20_11_BIT_UNDF);
		else if ( (i & DS18B20_10_BIT) == DS18B20_10_BIT ) 
			meas &= ~(DS18B20_10_BIT_UNDF);
		else { // if ( (i & DS18B20_9_BIT) == DS18B20_9_BIT ) { 
			meas &= ~(DS18B20_9_BIT_UNDF);
		}
	}			
	
	*cel  = (uint8_t)(meas >> 4); 
	*cel_frac_bits = (uint8_t)(meas & 0x000F);
	
	return DS18X20_OK;
}