On Thu, Aug 22, 2002 at 06:42:54PM +0200, Johan Fredriksson wrote:
> Hi,
>
> Well...I've been reading the datasheets a couple of time before sending
> this mail. I must say that it hasn't made me any wiser.
> My DS18S20 is used with +5, Gnd and signal so it should not be a need
> for a strong pullup. And as I can read the ROM ID I know it's connected
> correct.
>
> This is my code for reading the temp. In this code I tried with pullup also.
> As before all chars from DS2480B is read by the interrupt routine.

Well, I've never interfaced to a DS18S20 using the DS2480B.  But I
have recently written code to talk directly to a DS18S20 using
bit-banging 1-wire routines.  Here's a snippet that reads the
temperature.  OwReset sends a 1-wire reset pulse.  OwTouchByte
essentially writes a byte of data over a 1-wire link.  OwReadByte
reads a byte over a 1-wire link.

        call    OwReset
        btfss   OwPresence      ; Is presence set?
         goto   No1820          ; No...

        movlw   0xcc            ; Issue Skip ROM command
        call    OwTouchByte     ;  .

        movlw   0x44            ; Start temperature conversion
        call    OwTouchByte     ;  .

        delayS  2               ; Wait 2 seconds for conversion to complete
        call    OwReset         ; Reset again

        movlw   0xcc            ; Issue Skip ROM command
        call    OwTouchByte     ;  .

        movlw   0xbe            ; Read the temperature
        call    OwTouchByte     ;  .

        call    OwReadByte      ; Read 2 bytes, and store in tempL and tempH
        movwf   tempL
        call    OwReadByte
        movwf   tempH
        call    OwReset         ; We only care about the first 2
                                ; bytes, so abort the rest of the
                                ; transaction

It looks like you have the DS18S20 protocol correct.  So maybe you
have something wrong talking to the DS2480B.

-Dave

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