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PicBasic Experiments With The PIC16F877
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This application shows how to use the PIC16F877 to control, and interface with the Dallas DS1820 1-Wire™ Digital Thermometer. If you missed the LCD connection schematic for these experiments, click HERE.
This application shows how easy PicBasic makes it to communicate with smart peripherals such as the DS1820. To accomplish the exact same thing we're doing in this experiment in assembly language is like the difference between night & day. This is an excellent example of the pure simplicity of using PicBasic. Not to mention the huge time savings you'll have since you aren't required to spend all day hand coding all the little details in assembly language.
As shown above in figure 2, the connections are extremely simple. Just hook the center-pin of the DS1820 to Port C.0. The 4.7K pull-up resistor, and the DS1820 1-Wire™ Digital Thermometer are all you need besides the PIC16F877 to complete the circuit for this experiment. Here is the PicBasic code:
' Picbasic Pro program to read DS1820 1-wire temperature sensor
' and display temperature on LCD
' Define LCD pins
Define LCD_DREG PORTD
Define LCD_DBIT 4
Define LCD_RSREG PORTE
Define LCD_RSBIT 0
Define LCD_EREG PORTE
Define LCD_EBIT 1
' Allocate variables
command var byte ' Storage for command
i var byte ' Storage for loop counter
temp var word ' Storage for temperature
DQ var PORTC.0 ' Alias DS1820 data pin
DQ_DIR var TRISC.0 ' Alias DS1820 data direction pin
ADCON1 = 7 ' Set PORTA and PORTE to digital
Low PORTE.2 ' LCD R/W line low (W)
Pause 100 ' Wait for LCD to start
Lcdout $fe, 1, "Temp in degrees C"' Display sign-on message
' Mainloop to read the temperature and display on LCD
mainloop:
Gosub init1820 ' Init the DS1820
command = $cc ' Issue Skip ROM command
Gosub write1820
command = $44 ' Start temperature conversion
Gosub write1820
Pause 2000 ' Wait 2 seconds for conversion to complete
Gosub init1820 ' Do another init
command = $cc ' Issue Skip ROM command
Gosub write1820
command = $be ' Read the temperature
Gosub write1820
Gosub read1820
' Display the decimal temperature
Lcdout $fe, 1, dec (temp >> 1),".",dec(temp.0 * 5)," degrees C"
Goto mainloop ' Do it forever
' Initialize DS1820 and check for presence
init1820:
Low DQ ' Set the data pin low to init
Pauseus 500 ' Wait > 480us
DQ_DIR = 1 ' Release data pin (set to input for high)
Pauseus 100 ' Wait > 60us
If DQ = 1 Then
Lcdout $fe, 1, "DS1820 not present"
Pause 500
Goto mainloop ' Try again
Endif
Pauseus 400 ' Wait for end of presence pulse
Return
' Write "command" byte to the DS1820
write1820:
For i = 1 to 8 ' 8 bits to a byte
If command.0 = 0 Then
Gosub write0 ' Write a 0 bit
Else
Gosub write1 ' Write a 1 bit
Endif
command = command >> 1 ' Shift to next bit
Next i
Return
' Write a 0 bit to the DS1820
write0:
Low DQ
Pauseus 60 ' Low for > 60us for 0
DQ_DIR = 1 ' Release data pin (set to input for high)
Return
' Write a 1 bit to the DS1820
write1:
Low DQ ' Low for < 15us for 1
@ nop ' Delay 1us at 4MHz
DQ_DIR = 1 ' Release data pin (set to input for high)
Pauseus 60 ' Use up rest of time slot
Return
' Read temperature from the DS1820
read1820:
For i = 1 to 16 ' 16 bits to a word
temp = temp >> 1 ' Shift down bits
Gosub readbit ' Get the bit to the top of temp
Next i
Return
' Read a bit from the DS1820
readbit:
temp.15 = 1 ' Preset read bit to 1
Low DQ ' Start the time slot
@ nop ' Delay 1us at 4MHz
DQ_DIR = 1 ' Release data pin (set to input for high)
If DQ = 0 Then
temp.15 = 0 ' Set bit to 0
Endif
Pauseus 60 ' Wait out rest of time slot
Return
End
The DS1820 1-Wire Digital thermometer has a lot of extremely useful applications. For more information, or to download the complete datasheet for the DS1820, visit the Dallas Semiconductor web site. For your convenience, here is the link to the Dallas datasheet directory. Click HERE for the datasheet.... Get PicBasic:
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Copyright © 1999-2008 Reynolds Electronics |
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