DS1820 versus DS18S20

[gadelhas]

Hi,

I have a code that works great with the DS1820, however when i change to a DS18S20, the only thing that i get is 127.68ºC.

I allready made a search on the forum, however all the resaults are exactly the same as my code.

I have 2 DS18S20, and the show exactly the same value.

Can somebody help me;

Here is my code.

count_remain Var Byte			' Count remaining
count_per_c  Var Byte			' Count per degree C
temperature  Var Word



'                              REGISTOS PINOUT 1 = IN; 0 = OUT
' ===========================================================
        '76543210
TRISA = %11111111 
TRISB = %00001111 
TRISC = %00100000 
TRISD = %00000000 
TRISE = %00000000
ADCON1 = %00001110
ADCON0 = %00000000

'                              NOMES PINOUT
' ===========================================================
LED  VAR PORTC.3
DQ   VAR PORTD.0

'                              DEFENIÇÕES
' ===========================================================
 
   DEFINE LCD_DREG PORTB       ' LCD Data bits on PORTB
   DEFINE LCD_DBIT 4           ' PORTB starting address
   DEFINE LCD_RSREG PORTB      ' LCD RS bit on PORTB
   DEFINE LCD_RSBIT 3          ' LCD RS bit address
   DEFINE LCD_EREG PORTB       ' LCD E bit on PORTB
   DEFINE LCD_EBIT 2           ' LCD E bit address
   DEFINE LCD_BITS 4           ' LCD in 4-bit mode
   DEFINE LCD_LINES 2          ' LCD has 2 rows
   DEFINE LCD_COMMANDUS 2000   ' Set command delay time in us
   DEFINE LCD_DATAUS 50        ' Set data delay time in us

'                             INICIO PROGRAMA
' ===========================================================

Main:
   gosub Read_Sensor_Amp
   pause 100
goto Main

'                        LEITURA SENSOR AMPLIFICADOR
' ===========================================================

Read_Sensor_Amp:
OWOut DQ,1,[$CC,$44]
Waitloop: OWIn DQ,4,[count_remain]
If count_remain = 0 Then Waitloop
 OWOut DQ,1,[$CC,$BE]
 OWIn DQ,0,[temperature.LOWBYTE,temperature.HIGHBYTE,Skip 4,count_remain,count_per_c]
 temperature = (((temperature >> 1) * 100) - 25) + (((count_per_c - count_remain) * 100)/count_per_c)
Lcdout $fe, 1, " Temp. Amplificador "
Lcdout $fe, $C0,"      ",DEC (temperature/100),".",DEC2 temperature," C"
return
end

[gadelhas]

I think it's beacuse i'm using the DS18S20P. Can somebody confirm this?

[Darrel Taylor]

I think it's beacuse i'm using the DS18S20P. Can somebody confirm this?

I think that means it uses "Parasitic Power" only.

If so, you have to drive the DQ line HIGH for 750ms during the conversion.
After that you can read it like normal.
It doesn't get power from the VDD pin.

[biggej]

DT is on the right track but maybe for not exactly the right reason. The DS18S20 does not have to run with parisitic power but it can if needed. However this from Maxim..
"Specification Differences: The primary specification difference between the two parts is the temperature conversion time: DS1820 = 500ms (max) and DS18S20 = 750ms (max)."

I believe you may also be using "count remain" improperly to signal the end of conversion. End of conversiion may be determined by issing a "Read time slot" command until the result is non zero. (Yes, it is in the data sheet!) All that being said, you can probably get by with only adding the 750ms delay after the conversion command.
Jim

[Darrel Taylor]

DT is on the right track but maybe for not exactly the right reason. The DS18S20 does not have to run with parisitic power but it can if needed.

The DS18S20 doesn't, but the DS18S20P also called DS18S20-PAR, only uses "Parasitic Power".

The datasheet ...
http://datasheets.maxim-ic.com/en/ds/DS18S20-PAR.pdf

[biggej]

I should have know Darrel had it right!
It will take a wiring change to make Parasitic Power work too.
Jim