5: BASIC Stamp Command Reference – OWIN
BASIC Stamp Programming Manual 2.0c • www.parallaxinc.com • Page 203
The Demo Program uses a Dallas Semiconductor DS1820 Digital
Thermometer device connected as follows. Note that the 4.7 k
Ω pull-up
resister is required for proper operation.
Demo Program (I2C.bsp)
' This program demonstrates interfacing to a Dallas Semiconductor DS1820 1-wire Digital
' Thermometer chip using the BS2p's 1-wire commands. Connect the BS2p to the DS1820
' as shown in the diagram in the OWIN or OWOUT command description.
' This code reads the Counts Remaing and Counts per Degree C registers in the DS1820
' chip in order to provide a more accurate temperature reading (down to 1/100th of a
' degree). It also calculates degrees Fahrenheit. NOTE: The algebraic equations used
' will not work properly with negative temperatures.
'{$STAMP BS2p} 'STAMP directive (specifies a BS2p)
Temp VAR WORD 'Holds the temperature value
CRem VAR BYTE 'Holds the counts remaining value
CPerC VAR BYTE 'Holds the Counts per degree C value
Start:
OWOUT 0, 1, [$CC, $44] 'Send Calculate Temperature command
CheckForDone: 'Wait until conversion is done
PAUSE 25
OWIN 0, 4, [Temp] 'Here we just keep reading low pulses until
IF Temp = 0 THEN CheckForDone 'the DS1820 is done, then it returns high.
OWOUT 0, 1, [$CC, $BE] 'Send Read ScratchPad command
OWIN 0, 2, [Temp.LOWBYTE,Temp.HIGHBYTE,CRem,CRem,CRem,CRem,CRem,CPerC]
'Calculate temperature in degrees C
Temp = Temp>>1*100-25+((CPerC*100-(CRem*100))/CPerC)
DEBUG HOME, DEC3 Temp/100, ".", DEC2 Temp-(Temp/100*100), " C", CR
'Calculate temperature in degrees F
Temp = Temp*/461+3200
DEBUG DEC3 Temp/100, ".", DEC2 Temp-(Temp/100*100), " F"
GOTO Start
2
Figure 5.20: DS1820 Circuit.
NOTE: The 4.7 k
Ω resister is
required for proper operation.
Vss
Vdd
P0
DS1820
(PR35)
4.7 k
Ω
DQ
1 2 3
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