DS1820 and 18f2550


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  1. #1
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    Thanks for your help mate,

    I tried using your code but my problem is earlier on than the number of bytes being read. I put this 'turn LED line on' line after the wait loop. The LED never comes on. My ds1820 is never being ready I guess. I have double checked wiring. I know it's an odd one. Any more ideas just to get me past the wait loop. Once I am past there I can work the rest out from your fabulous info!

    If NOT DQ Then waitloop
    high PORTA.5
    ' the LED never comes on (but of course it does if I put the line before the loop!)

    Regards

    Rich

  2. #2
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    Ok,

    Reading closer the datasheet shows there are time slots for writing and reading ...

    so, rub out your PAUSE 2000 ...

    but keep on polling DQ !

    Alain
    Last edited by Acetronics2; - 2nd October 2007 at 14:11.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  3. #3
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    Thanks again mate but your code, the code I tried last, didn't have a pause 2000. That was mine. Your code never gets past the wait loop either. Here is code again for clarity. I appreciate it isn't going to work later in code as I haven't done anything with offset etc but there is no point till I get past the wait loop for ds1820 to become ready.

    Code:
    define OSC 48
    ADCON1 = 7            ' Set PORTA to digital
    DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
    DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
    DEFINE HSER_CLROERR 1 ' Clear overflow automatically
    DEFINE HSER_SPBRG 225 ' 9600 Baud @ 48MHz, 0.0%
    SPBRGH = 4
    BAUDCON.3 = 1         ' Enable 16 bit baudrate generator
    HSEROUT [13,10,"Starting"]
    
    DQ var PORTA.0
    temperature var word
    count_remain var word
    count_per_c var word
    offset var word
    '************************************************* ****************************
    ' Start temperature conversion
    '************************************************* ****************************
    
    mainloop: OWOut DQ, 1, [$CC, $44 ]
    
    '************************************************* ****************************
    ' Check for still busy converting ( ~ 4500 times ... )
    '************************************************* ****************************
    
    waitloop:
    
    INPUT DQ
    If NOT DQ Then waitloop
    
    high PORTA.5 ' turn on LED if it gets past this point
    
    '************************************************* ****************************
    ' Read the temperature
    '************************************************* ****************************
    
    OWOut DQ, 1, [$CC, $BE ]
    
    OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]
    
    '************************************************* ****************************
    ' Calculate temperature in degrees C to 2 decimal places (not valid for negative temperature)
    '************************************************* ****************************
    
    temperature = (((temperature >> 1) * 100) - 25) + (((count_per_c - count_remain) * 100) / count_per_c)+ offset
    
    Lcdout $fe, 1, DEC (temperature / 100), ".", DEC2 temperature, " ",$DF,"C"
    
    '************************************************* ****************************
    ' Calculate temperature in degrees F to 2 decimal places (not valid for negative temperature)
    '************************************************* ****************************
    
    temperature = (temperature */ 461) + 3200
    'Lcdout $fe, $c0, DEC (temperature / 100), ".", DEC2 temperature, " ",$DF,"F"
    HSEROUT [13,10, " Temp = ",DEC (temperature / 100), ".", DEC2 temperature, " ","F"]
    goto mainloop

  4. #4
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    Try ADCON1 = 15 VS ADCON1 = 7. You are leaving most of PORTA setup as analog inputs.
    Regards,

    -Bruce
    tech at rentron.com
    http://www.rentron.com

  5. #5
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    Did you disable Porta Comparators ??? looks no ...

    Default setting ... ok, but ...

    EXAMPLE 10-1: INITIALIZING PORTA

    CLRF PORTA ; Initialize PORTA by
    ; clearing output
    ; data latches
    CLRF LATA ; Alternate method
    ; to clear output
    ; data latches
    MOVLW 0Fh ; Configure A/D
    MOVWF ADCON1 ; for digital inputs
    MOVLW 07h ; Configure comparators
    MOVWF CMCON ; for digital input

    MOVLW 0CFh ; Value used to
    ; initialize data
    ; direction
    MOVWF TRISA ; Set RA<3:0> as inputs
    ; RA<5:4> as outputs

    Even Microchip does it !!! ...

    Alain
    Last edited by Acetronics2; - 2nd October 2007 at 17:11.
    ************************************************** ***********************
    Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
    ************************************************** ***********************
    IF there is the word "Problem" in your question ...
    certainly the answer is " RTFM " or " RTFDataSheet " !!!
    *****************************************

  6. #6
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    Bruce/Alain THANKYOU SO MUCH!!

    The ADCON1=15 did it and I also tried your ASM example Alain. They both fixed it. Sorry, I am new to this (well, 2 weeks new) and keep thinking I have the hang of it then learning more! I thought ADCON1=7 had disabled analogue inputs on all pins. I'll read that bit of DS before I go to bed so I have actually learnt it rather than having been spoon fed! Thanks!! OK, read it and learnt something very important. The DS is the bible, if only I could understand it!

    Just read example 10.1. For the first time ever the example makes some sense to me and I can see why it is relevant to us PBPers. Wow!

    I was just about to go to bed miserable. I got USB going today, wanted to feed temperature to VB instead of just my name. So much is coming together! 24LC256 challenge tomorrow!

    Now I can wake up to a new day and a new phase of project!

    THANKS SO MUCH
    Rich

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