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cschwemin
Joined: 28 Jul 2009
Posts: 3
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 Posted: Mon Aug 17, 2009 1:38 pm Post subject: lsb and msb ? could someone explain please |
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Hello
I have been reading the Datasheet for the ds18b20 and would like to know what the Definition for LSB and MSB are. did a search on google and came up empty handed. any info would be great.
thanks
Datasheet http://www.spezial.com/doc/maxim/ds18b20.pdf |
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MAK399
Joined: 23 Jun 2009
Posts: 110
Location: Germany
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| Posted: Mon Aug 17, 2009 2:20 pm Post subject: |
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Hi,
least significant byte (LSB) = right byte of the Interger Value = Byte0 of Scratchpad
Most significant byte (MSB) = left byte of the Integer Value = Byte1 of Scratchpad
For Example: 85 C
MSB = 0000 0101 LSB = 0101 0000
MAK399
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mattcro
Joined: 03 Oct 2007
Posts: 327
Location: Scotland
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| Posted: Mon Aug 17, 2009 3:55 pm Post subject: |
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Often LSB and MSB mean least/most significant BIT of a register or variable, but it can also refer to least/most significant byte (eg of a multi-byte variable such as integer or long).
The least significant bit is the rightmost like in mak399's description.
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BascomAVR 2.0.8.5 |
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cschwemin
Joined: 28 Jul 2009
Posts: 3
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| Posted: Tue Aug 18, 2009 2:37 am Post subject: |
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Thanks for the quick reply, now i have more questions  I have gone over the source code from here http://www.mcselec.com/index.php?option=com_content&task=view&id=75&Itemid=57 and searched the forums repeatedly. but i am still having no luck with this temperature sensor. all of the examples have so many things i dont really need, like CRC checks, multiple sensors and several decimal places. i am trying to measure a range from 0 to a max of 200~250 degrees Fahrenheit. but i get really bogged down as i am very new to this. This is the source code from what i have written so far. any help would be greatly appreciated.
| Code: |
'=============================================================================='
'This is a single sensor temperature monitor using the DS18B20. The ATMega32 ' '
'Sends all data back through rs232. ' '
' '
'Author: Chris Schwemin '
'E-Mail: Cschwemin@marquettewind.com '
'08-17-2009 '
' '
'=============================================================================='
$regfile = "m32def.dat"
$crystal = 16000000
$baud = 9600
'Sub routine to start temp conversion on DS18B20
Declare Sub Convertt
'Tell 1wire to use Port C and Pin 1
Config 1wire = Portc.1
'Array for holding data from DS18B20
Dim Sc (9) As Byte
'Variables
Dim Temperature As Byte
Do
'start conversion
Convertt
'Using 2wire bus, no longer delay is needed
Waitus 200
1wwrite &HBE
Sc (1) = 1wread(9)
Temperature = Sc (1)
Print Temperature
Wait 2
Loop
Sub Convertt
'Bus Reset
1wreset
'Skip ROM checking " only one device connected"
1wwrite &HCC
'Convert the Temp
1wwrite &H44
End Sub
'Borrowed some comments from Göte Haluza, Thanks 
'DALLAS DS18B20 ROM and scratchpad commands''''''''''''''''''''''''''1wwrite....
'&H 33 read rom - single sensor
'&H 55 match rom, followed by 64 bits
'&H CC skip rom
'&H EC alarm search - ongoining alarm >TH <TL
'&H BE read scratchpad
'&H 44 convert T
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I have compiled other sources and have verified the wiring to be correct and the devices to work as intended.
-Chris
Bascom ver 1.11.95 |
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cschwemin
Joined: 28 Jul 2009
Posts: 3
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| Posted: Tue Aug 18, 2009 2:38 am Post subject: |
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| Also i have really tried to not come to the forums for help on this as i see alot of topics and i know how annoying the same questions can be over and over again but i ran out of options. your patience is greatly appreciated |
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MAK399
Joined: 23 Jun 2009
Posts: 110
Location: Germany
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| Posted: Tue Aug 18, 2009 7:16 am Post subject: |
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Hello,
have you also tried the code from Luciano ?
You can find it here:
http://www.mcselec.com/index2.php?option=com_forum&Itemid=59&page=viewtopic&t=3993&highlight=ds18b20
It is in my opinion easier to understand and it uses by default no CRC
All Values comming from this sensors are in Celsius.
Conversion from Celsius in Fahrenheit = (( Temp Celsius × 9 ) / 5 ) + 32
The default resolution = 12 Bit and with this resolultion you have to wait
750ms between starting the conversion and reading the scratchpad (where only Byte0 and Byte1 is interesting for you)
MAK399
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MAK399
Joined: 23 Jun 2009
Posts: 110
Location: Germany
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| Posted: Tue Aug 18, 2009 7:27 am Post subject: |
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I forgot to mention that you reading only Byte0 of Scratchpad but the default resolution is 12 Bit so you only read 8Bit from 12Bit of the temperature.
Your Temperature should be Integer Value because the minimun resolution = 9Bit. You always need the second Byte of the Integer Value to store the 9th Bit when you prgroam the DS18B20 to use 9Bit resolution.
MAK399
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