Handy
Tips - Dallas 1 Wire Protocol
Also see the
following projects for more information/examples on 1-Wire
Communication;
1-Wire
is a device communications bus system designed by Dallas
Semiconductor that provides low-speed data, signaling and power over
a single wire (a Ground wire is also needed). 1-Wire is similar in
concept to I²C, but with lower data rates and a much lower cost. It
is typically used to communicate with small inexpensive devices such
as digital thermometers, weather instruments etc.
Devices are laser programmed with a 64 bit code that contains its
unique information. This includes its Family Code, Address
Information, and a CRC checksum value for integrity checking. You
don't need to use the 64 bit address to talk to most devices when
they are the only ones on the databus, however you must when there
is more than one.
To ascertain what 64 bit address a component has, use this example;
Device 16f877
XTAL 4
Declare LCD_TYPE ALPHA
' Type of LCD Used is Alpha
Declare LCD_DTPIN PORTB.4
' The control bits B0,B1,B2,B3
Declare LCD_RSPIN PORTB.2
' RS pin on B4
Declare LCD_ENPIN PORTB.3
' E pin on B5
Declare LCD_LINES 2
' Amount of LCD lines
Declare LCD_INTERFACE 4
' Interface method is 4 bit
PORTB_PULLUPS = true
ALL_DIGITAL = TRUE
SYMBOL DQ = Portb.0
' 1-Wire databus
DIM ID1 AS BYTE
DIM ID2 AS BYTE
DIM ID3 AS BYTE
DIM ID4 AS BYTE
DIM ID5 AS BYTE
DIM ID6 AS BYTE
DIM ID7 AS BYTE
DIM ID8 AS BYTE
Delayms 150
CLS
Again:
OWRITE DQ, 1,[$33]
' Request ROM information
OREAD DQ,0,[ID1,ID2,ID3,ID4,ID5,ID6,ID7,ID8]
' Store the response
Print at 1,1,"Fam= ",HEX2 ID1, " CrC= ", HEX2 ID8
Print at 2,1,"ID= ", HEX2 ID2, HEX2 ID3,HEX2 ID4,HEX2 ID5,HEX2
ID6,HEX2 ID7
Goto Again
Be sure to
place the pull-up
resistor on the databus. On a side note, I have
had problems with 1-Wire data transfer from PORTA, even with the
ALL_DIGITAL = TRUE declaration, so I wouldn't recommend any pins on
PORTA for 1-Wire data transfer.
Click here to see this circuit in action!
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