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DS1620 thermometer — Parallax Forums

DS1620 thermometer

KiwiKiwi Posts: 85
edited 2005-03-29 13:59 in General Discussion
hello,

I have added a DS1620 into my application. I now can read the data out of the DS1620. I have a little problem of converting the·tempvalue (2complement)·into degrees. Does anybody have any suggestion of how it shoud be done. I am not USSING SX/B nut plain Sx - intructions.

Thanks

Kurt

Comments

  • BeanBean Posts: 8,129
    edited 2005-03-25 14:19
    To convert 2's complement.
    Invert all bits (XOR $FF), then add 1 (INC).

    For example 255 invert all bits gives 0, then add 1 gives 1 (255=-1)

    Another good way to learn, is to write a very simple SX/B program that does what you want. Then compile it and look at the output.

    Bean.

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  • Stanley FredericksonStanley Frederickson Posts: 19
    edited 2005-03-26 07:03
    I haven't tried this personally since I don't have a DS1620.· I am basing this on the Maxim datasheet.

    ; I am going to assume that you have loaded the 9-bit temperature
    ; value into the following two 8-bit registers
    temp_hi···ds·1·; HI byte - only care about the least signifcant bit of this byte
    temp_lo···ds·1·; LO byte
    ; The code below will take the 9-bit value in temp_hi and temp_lo and create
    ; a signed magnitude value in the following two variables
    temp_sign··=·temp_hi.0·; Least significant bit of temp_hi will be used as sign bit
    temp_magnitude·= ·temp_lo··; Will re-use the lower byte as the magnitude

    ; Read the temperature into temp_hi and temp_lo with your existing code

    ; If the most significant bit of the 9-bit temperature is set
    ; then you have a negative value so the magnitude needs to be inverted
    ··sb temp_sign
    ··jmp [noparse]:p[/noparse]ositive_temp··; Sign-bit not set so the value is positive
    ··not temp_magnitude··; Value is negative so invert the magnitude portion
    ··inc temp_magnitude
    [noparse]:p[/noparse]ositive_temp

    ; The DS1620's resolution is 1/2 degree Celcius so you need to divide the magnitude
    ; by 2 (shift right by 1) to get the value of the temperature in degrees
    ··clc
    ··rr temp_magnitude··; temp_magnitude now has temp in degrees
    ; If you want, you can look at the carry flag for 0.5 degree accuracy
    ;· Carry set means that the temperature ends with .5
    ;· Carry clear means that the temperature ends with .0
  • KiwiKiwi Posts: 85
    edited 2005-03-29 05:57
    Hello,

    That is what i did, but i have the impression that somethings is wrong during the shift in of the Data that comes from the ds1620. Even when i read the controlregister, it was set for 3 wire communication $02, i get something back like $88.

    I will take a further look into the program, and i can figure it out i will post it

    Thanks

    Kurt
  • KiwiKiwi Posts: 85
    edited 2005-03-29 13:59
    i have the impression that everything is working fine, i forgot BANK instructions in some subroutines



    Kurt
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