Hot!CRC problem

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kishor009
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Re: CRC problem 2017/09/12 03:39:12 (permalink)
0
poly = 0xA001
 
#21
kishor009
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Re: CRC problem 2017/09/12 03:41:50 (permalink)
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Alpha Whisky
As you obviously can't be bothered to do even the simplest google search I'm not sure why I'm posting this, but:
 
https://www.lammertbies.nl/comm/info/crc-calculation.html
 




but i m use different poly
#22
Alpha Whisky
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Re: CRC problem 2017/09/12 03:44:50 (permalink)
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What do you think
CRC-16 (Modbus)
is?
#23
kishor009
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Re: CRC problem 2017/09/12 03:48:11 (permalink)
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yes
#24
Alpha Whisky
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Re: CRC problem 2017/09/12 03:51:27 (permalink)
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That wasn't a yes/no question.
#25
kishor009
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Re: CRC problem 2017/09/12 04:02:31 (permalink)
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Alpha Whisky
That wasn't a yes/no question.


sorry
then??
#26
Alpha Whisky
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Re: CRC problem 2017/09/12 04:06:13 (permalink)
+1 (1)
Select input type "hex". Type in your message bytes. Click "Calculate CRC". Read the CRC. Don't forget that mobus sends the CRC little endian.
#27
kishor009
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Re: CRC problem 2017/09/12 04:28:47 (permalink)
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Alpha Whisky
Don't forget that mobus sends the CRC little endian.




what?
#28
1and0
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Re: CRC problem 2017/09/12 04:31:30 (permalink)
+2 (2)
kishor009
Alpha Whisky
Don't forget that mobus sends the CRC little endian.

what?

I see that coming: https://en.wikipedia.org/wiki/Endianness
post edited by 1and0 - 2017/09/12 04:33:23
#29
qhb
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Re: CRC problem 2017/09/12 05:39:59 (permalink)
+1 (1)
This user plainly does not have the experience to implement MODBUS by himself, and in all likelihood does not need MODBUS protocol at all, but he always clams up when you ask why it has to be MODBUS.
 
#30
Alpha Whisky
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Re: CRC problem 2017/09/13 00:43:23 (permalink)
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Inexperience isn't the problem, we all had to start somewhere. It's the complete unwillingness to do the slightest bit of independent study or research that gets me, he just wants to be spoon-fed everything.
#31
Jim Nickerson
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Re: CRC problem 2017/09/13 06:48:23 (permalink)
+2 (2)
I think it is a language problem (ESL).
He is doing the best he can, he does not understand the words.
#32
1and0
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Re: CRC problem 2017/09/13 11:23:31 (permalink)
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Maybe... but English is one of the official languages in India.
#33
dan1138
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Re: CRC problem 2017/09/13 12:36:32 (permalink)
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In defense for the Original Poster there is a crap load of bad information on CRC computation and usage. It gets worse with when trying to make sense of some of the stranger implementation choices.
 
The MODBUS implementation presents a special challenge as the choice of CRC calculation (forward or reverse) depends on the bit order of the transport stream. This is an issue because the MODBUS transport can be asynchronous serial that sends the Least Significant Bit first, I2C where the Most Significant Bit is sent first, SPI where MSB first is common but on occasion LSB fist may be seen. Then there are the parallel implementations of MODBUS where no bit serial transport is used at all. Through all these transport streams the same CRC is used. At its best the CRC for MODBUS is effective at it worst it is not much better than a checksum.
 
As a specific example of where confusion will ensue consider this project:
 
Design a MODBUS transport bridge between a MODBUS segment using an I2C transport stream to a MODBUS segment using an asynchronous serial transport steam.
 
The problem with selecting the CRC calculation method that is correct for the transport stream results in CRC that are different for MODBUS packets that are otherwise identical. This is the result of serial transport streams that send data in different bit orders.
post edited by dan1138 - 2017/09/13 16:36:44
#34
kishor009
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Re: CRC problem 2017/09/13 21:52:03 (permalink)
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JANickerson
I think it is a language problem (ESL).
He is doing the best he can, he does not understand the words.




right
i use google translate
#35
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