DS1820 and 18f2550

[rjones2102]

There are so many threads/ articles on the net about this but I am still failing to get it working. If anyone has a good idea, please HELP ME!

I have the DS1820 wired with 5 volts on pin 3, a 4.7 k pullup on pin 2 to PortA.0 on Pic and pin 1 to gnd. I have measured voltages with and without the 18f2550 in place to verify the voltage on pin 3 of DS1820 is coming from pullup. I am 99.999% certain electrically it is all good.

My fuse are setup as follows as I have USB comms running but not for the duration of the DS1820 tests just to make it simple. I am using a 20Mhz OSC and USB comms works fine so I am confident about Osc config etc at least for USB. OW doesn't have any special requirements does it?.

	__CONFIG    _CONFIG1L, _PLLDIV_5_1L & _CPUDIV_OSC1_PLL2_1L & _USBDIV_2_1L  
                            ;              ; USB clock source comes from the 96 MHz PLL divided by 2
                            ;              ; [OSC1/OSC2 Src: /1][96 MHz PLL Src: /2]
                            ; No prescale (4 MHz oscillator input drives PLL directly)

	__CONFIG    _CONFIG1H, _FOSC_HSPLL_HS_1H & _FCMEN_OFF_1H & _IESO_OFF_1H 
                            ;                  ;               ; Oscillator Switchover mode disabled
                            ;                  ; Fail-Safe Clock Monitor disabled
                            ; XT oscillator, PLL enabled, XT used by USB
                            
	__CONFIG    _CONFIG2L, _PWRT_ON_2L & _BOR_ON_2L  & _BORV_2_2L  & _VREGEN_ON_2L   
	__CONFIG    _CONFIG2H, _WDT_OFF_2H 
	__CONFIG    _CONFIG3H, _MCLRE_ON_3H & _LPT1OSC_OFF_3H & _PBADEN_OFF_3H & _CCP2MX_ON_3H 
	__CONFIG    _CONFIG4L, _STVREN_ON_4L & _LVP_OFF_4L & _XINST_OFF_4L & _DEBUG_OFF_4L

I have tried 2 pieces of code. First one just outputs
Busy
Busy
Busy
.....

To Hyperterm:

DEFINE      OSC 48          ' We're using a 20MHz oscillator
ADCON1 = 7 ' Make pins 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"]
Comm_Pin    VAR	PortA.0     ' One-wire Data-Pin "DQ" on PortC.0
Busy        VAR BIT         ' Busy Status-Bit
R_Temp      VAR	WORD        ' RAW Temperature readings
TempC       VAR WORD        ' Temp in deg C
TempF       VAR WORD        ' Temp in deg F
Float       VAR WORD        ' Holds remainder for + temp C display
Cold_Bit    VAR R_Temp.Bit11' Sign-Bit for +/- Temp. 1 = Below 0 deg C
Real_Cold   CON 1           ' Define Real_Cold = 1
BAUD        CON 16468       ' N9600 for serial LCD
DISP        VAR PortB.0     ' Pin to drive serial LCD
Deg         CON 223         ' Data to display Deg ° symbol
CLR         CON 1           ' CLR LCD command
LINE1       CON 128         ' LCD line #1
LINE2       CON 192         ' LCD line #2
LINE3       CON 148         ' LCD line #3
LINE4       CON 212         ' LCD line #4
INS         CON 254         ' LCD command mode parameter
Sign        VAR BYTE        ' +/- sign for temp display
Dummy       VAR BYTE        ' Dummy for Div32

Start_Convert:
    OWOUT   Comm_Pin, 1, [$CC, $44]' Skip ROM search & do temp conversion
    Pause 2000    
Wait_Up:
    OWIN    Comm_Pin, 4, [Busy]    ' Read busy-bit
    hserout [13,10,"Busy"]
    pause 100
    IF      Busy = 0 THEN Wait_Up  ' Still busy..?, Wait_Up..!
    OWOUT   Comm_Pin, 1, [$CC, $BE]' Skip ROM search & read scratchpad memory
    OWIN    Comm_Pin, 2, [R_Temp.Lowbyte, R_Temp.Highbyte]' Read two bytes / end comms
    GOSUB   Convert_Temp
    GOTO    Start_Convert
    
Convert_Temp:                 ' +32.0 to +257 F 
    IF      Cold_Bit = Real_Cold THEN Yikes ' If Cold_Bit = 1, it's below "0" deg C
    Sign  = "+"
    Dummy = 625 * R_Temp      ' Multiply to load internal registers with 32-bit value
    TempC = DIV32 10          ' Use Div32 value to calculate precise deg C
    Dummy = 1125 * R_Temp
    TempF = DIV32 100
    IF TempF >6795 THEN ' Over 99.5 deg F..?
       TempF = TempF + 3200
       HSEROUT [13,10, " TempF = ",Sign,DEC TempF DIG 4,_
       DEC TempF DIG 3,DEC TempF DIG 2,".",DEC2 TempF,Deg,"F "]
    ELSE
       TempF = TempF + 3200
       HSEROUT [13,10, " TempF = ",Sign,DEC TempF DIG 3,_
       DEC TempF DIG 2,".",DEC2 TempF,Deg,"F "]
    ENDIF
    TempC  = (R_Temp & $0FF0) >> 4 ' Mask middle 8-bits, shift into lower byte
    Float = ((R_Temp.Lowbyte & $0F) * 625) ' Lower 4-bits of result * 625
    HSEROUT [13,10, " TempC = ",Sign,DEC TempC,".",DEC Float,Deg,"C "]
    HSEROUT [13,10, "Raw", IBIN16 R_Temp]
    RETURN

Yikes:                      ' Display full range -C to -F conversion
    Sign   = "-"            ' Display - symbol for negative temp
    Dummy  = 625 * ~R_Temp+1' Multiply to load internal registers with 32-bit value
    TempC  = DIV32 10       ' Use Div32 value to calculate precise deg C
    TempF  = ~R_Temp / 16   ' Begin conversion from -C to deg +/-F
    IF TempF >=18 THEN      ' Check for -degrees F "-18 C = -0.4 F"
       TempF   = ((((TempF + 50) * 9) /5) -122) ' -C to -F below -17 deg C
       HSEROUT [13,10, " TempF = ",Sign, DEC TempF,Deg,"F     "]
       HSEROUT [13,10, " TempC = ",Sign,DEC TempC DIG 4,_
       DEC TempC DIG 3,".",DEC3 TempC,Deg,"C "]
       HSEROUT [13,10, "Raw", IBIN16 R_Temp]
    ELSE                    ' Else result = +deg F
       TempF   = ((((-TempF + 50) * 9) /5) -58)' -C to +F below 32.0 deg F to -17 deg C
       HSEROUT [13,10, " TempF = ","+",DEC TempF,Deg,"F     "]
       HSEROUT [13,10, " TempC = ",Sign,DEC TempC DIG 4,_
       DEC TempC DIG 3,".",DEC3 TempC,Deg,"C "]
       HSEROUT [13,10, "Raw", IBIN16 R_Temp]
    ENDIF
    RETURN
    
    END

The second really simple bit of code just outputs 00.0

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
temp var word

loop:
owout DQ,1,[$cc]
owout DQ,0,[$44]
Pause 2000
owout DQ,1,[$cc]
owout DQ,0,[$be]
owin DQ,0,[temp.byte0,temp.byte1]
temp=temp*5
HSEROUT [13,10, " Temp = ",DEC2 temp/10,".", dec1 temp," ","C"]
goto loop

These bits of code come from sources that swear they work. What else could it be?!?!! For now I will try and send something else down USB to VB!!

Hope someone can help.

Thanks a lot

Rich