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HDC2010: Regarding the statement "the 2 LSBs D1 and D0 are always 0"

Vishnu Beema
Expert 1450 points
Part Number: HDC2010
Other Parts Discussed in Thread: HDC1080

Hello,

I have gone through SNAA312 application note. I am bit confused with the statement "the 2 LSBs D1 and D0 are always 0".

1) Whether D0 and D1 are lower two bits in TEMPERATURE[15-0] or lower two bits of TEMPERATURE[15-8] MSB.

When I read temperature I am getting below values. Where D0 and D1 of TEMPERATURE[15-8] MSB is always 0.

25775 : 0x64AF : 0110 0100 1010 1111

25783 : 0x64B7 : 0110 0100 1011 0111

25794 : 0x64C2 : 0110 0100 1100 0010

2) Even examples in SNAA312 is misleading.

TEMPERATURELSB = 0x293B

10555 : 0x293B : 0010 1001 0011 1011    Where both D0 & D1 in TEMPERATURE[15-0] and TEMPERATURE[15-8] are not zero.

HUMIDITYLSB = 0x42DC

17116 : 0x42DC : 0100 0010 1101 1100    Where D0 & D1 in TEMPERATURE[15-8] are not zero.

To avoid all these confusions, better to mark D0 and D1 in register descriptions itself.

3) To cross-check, I changed resolution settings. Previously I used 0x01 to trigger measurement with 14-bit resolution. Now I changed to 0xA1 to trigger measurement with 8-bit resolution. But I am getting 

For Temperature 

25950 : 0x655E : 0110 0101 0101 1110    Where both D0 & D1 in TEMPERATURE[15-0] and TEMPERATURE[15-8] are not zero.

 

I am bit confused with 14-bit / 8-bit resolution and with the statement "the 2 LSBs D1 and D0 are always 0".

 

Thanks & Regards

Vishnu Beema

  • 0
    TI__Guru* 91206 points

    Dear Vishnu - 

    I agree that wording is confusing and most likely a typo of some type - as there is no way for those bits to be 0 all the time. 0xFD 0xFD from the temp registers would only get you to range of 123.7034C...the device does have to indicate all the way to 0xFF 0xFF then, which allows the range of the device to be expressed (this is 124.9975C). in looking back to older devices like the HDC1080, this looks alot like may have been copied over inadvertently. I will work with the documentation folks to get this updated/corrected. 

    WRT to 8 bit vs 14 bit resolution - the difference here that you would see between them is the step size between hex values output would get bigger. 

  • 0 in reply to Josh Wyatt
    Expert 1450 points

    Thanks a lot for clarifying.

    Even in SNAA312 its mentioned as "the 2 LSBs D1 and D0 are always 0". 

    Last query on this, can you please give more details on your statement. Bit confused with highlighted below.

    "WRT to 8 bit vs 14 bit resolution - the difference here that you would see between them is the step size between hex values output would get bigger. "

    Is this same as my "Understanding-1" in below link.

    https://e2e.ti.com/support/sensors/f/1023/p/808666/2992588#2992588

    Thanks & Regards

    Vishnu Beema

  • 0 in reply to Vishnu Beema
    TI__Guru* 91206 points

    Dear Vishnu - 

    in the HDC1080 the registers are like this, and where that wording came from in the first place, I think: 

  • 0 in reply to Josh Wyatt
    Expert 1450 points

    Thank you for confirmation