We've had perfect results with the DS1822+, even when using it in parasitic (no VCC) mode. On Mon, Aug 10, 2009 at 6:33 AM, Marc Nicholas wrote: > At a guess, I'd say that you have it set to higher than 9-bit resolution? > AFAIK, the DS1822 has user configurable 9 to 12-bit resolution. > > -marc > > On Mon, Aug 10, 2009 at 9:23 AM, jim wrote: > >> All, >> >> I worked yesterday getting my one wire routines working, which I >> accomplished. >> The 1822 One Wire Temp Sensor is a 9 bit sensor. =A0It has a range of -5= 5C to >> +125C. >> It uses 2's complement math for the negative temps. =A0It's temperature >> measurement is >> contained in 2 bytes. =A0The LSB is the temp reading in .5C increments. = =A0The >> MSB is the >> sign bit. =A0All 8 positions in the MSB are sign bits. =A0So, I gather t= hat if >> the temp is negative, >> all 8 bits of the MSB would be set. =A0 However, when the PIC reads the = =A0Temp >> sensor, I get >> the correct (approximately) reading in the LSB, but the MSB has 1 or 2 b= its >> set. =A0It's not >> clear to me from the datasheet whether all 8 bits should be set for >> negative temps, or if it can >> be any number of bits set for negative temps. >> >> Does anyone have any experience with one wire comms, especially with this >> temp sensor? >> If so, do you have any idea about the MSB and how the sign bit is suppos= ed >> to work? >> Or any other insight that may give me an idea if I'm doing anything wron= g. >> >> BTW, I've tried powering this sensor from Vdd and using parasite power, = and >> it acts the same either way. >> Also, I opowered it from 5 volts and from 3 volts, and that doesn't chan= ge >> anything either. >> >> Please advise. >> >> >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 = =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0Thanks >> and Regards, >> >> >> =A0 Jim >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist