How to calculate the checksum?

[Guest]

Hi,

how can I calculate the checksum (CRC-16) from the byte[] I retrieve from a
hardware device through the RS232 serial port?

Christian

 

[Morten Wennevik [C# MVP]]

Hi Christian,

Maybe this articles can give you some ideas.

[CRC Encoding]
http://www.codeproject.com/csharp/marcelcrcencoding.asp?df=100&forumid=29803&exp=0&select=1726104

Hi,

how can I calculate the checksum (CRC-16) from the byte[] I retrieve from a
hardware device through the RS232 serial port?

Christian

 

[Guest]

how can I calculate the checksum (CRC-16) from the byte[] I retrieve from a
hardware device through the RS232 serial port?

I have some CRC-16 code on the shelf.

I fact I have more than one version.

Do you have some sample data and an expected result to
help determine which ?

Arne

 

[Guest]

Hi Arne,

thanks for your help. I have the following informations:

<Sync_1 = 0x81> 8 DATA-BITS No Parity
<Sync_2 = 0x82> 8 DATA-BITS No Parity
<Cksum> = Telegramm<[pos_Sync_1]> XOR . XOR . XOR ... [<pos_Sync_2-2>]
<Cmd> = Command to modem

|<--- CheckSum : --------------- XOR ------------------->|
<Sync_1>, <DEV_ADR>, <Cmd>, <OPTION>, [<DATA>], <Chksum>, <Sync_2>

Hope this helps.
Christian

how can I calculate the checksum (CRC-16) from the byte[] I retrieve from a
hardware device through the RS232 serial port?

I have some CRC-16 code on the shelf.

I fact I have more than one version.

Do you have some sample data and an expected result to
help determine which ?

Arne

 

[Peter Ibbotson]

Hi Arne,

thanks for your help. I have the following informations:

<Sync_1 = 0x81> 8 DATA-BITS No Parity
<Sync_2 = 0x82> 8 DATA-BITS No Parity
<Cksum> = Telegramm<[pos_Sync_1]> XOR . XOR . XOR ... [<pos_Sync_2-2>]
<Cmd> = Command to modem

|<--- CheckSum : --------------- XOR ------------------->|
<Sync_1>, <DEV_ADR>, <Cmd>, <OPTION>, [<DATA>], <Chksum>, <Sync_2>

It depends on what sort of CRC it is.

For most serial protocols it is based on the table driven one in x/y/zmodem
source code. However that isn't the correct CRC value for an ethernet packet
OR an SDLC/HDLC comms protocol.

You could use
http://sourceforge.net/projects/classlesshasher/?format=raw

which contains more CRC variants than I've encountered in the wild but most
comms protocols tend to use the one contained in FCS16.

I suspect from your code that actually you just want to XOR all the bytes in
the data together.

Without a sample data packet (or sample source code) it's nearly impossible
to tell if you've got it right. When I first did the ethernet one I ended up
hand decoding a packet on an oscilloscope screen to see exactly what was
transmitted!

Peter

 

[Guest]

thanks for your help. I have the following informations:

<Sync_1 = 0x81> 8 DATA-BITS No Parity
<Sync_2 = 0x82> 8 DATA-BITS No Parity
<Cksum> = Telegramm<[pos_Sync_1]> XOR . XOR . XOR ... [<pos_Sync_2-2>]
<Cmd> = Command to modem

|<--- CheckSum : --------------- XOR ------------------->|
<Sync_1>, <DEV_ADR>, <Cmd>, <OPTION>, [<DATA>], <Chksum>, <Sync_2>

Hope this helps.

That is not sample data and sample checksum.

It looks more as simple XOR than CRC.

But without more specific information everything will just
be guesswork.

Arne