CNAOB-Communications-Protocol-Notes: Difference between revisions

From *** My Personal Wiki ***
Jump to navigation Jump to search
← Older edit
Embeddedrf (talk | contribs)
1,247 edits
No edit summary
No edit summary
 
(15 intermediate revisions by one other user not shown)
Line 1: Line 1:


== CNAOB Serial Port Configuration ==
== Comm Port Binary Mode ==


Each message consists of 1 start bit (0), 8 data bits and 2 stop bits (1).
Is necessary to use binary mode.  Serial port in ASCII mode chokes on null = chr(0) chars


*[http://www.codenewsgroups.net/group/microsoft.public.vb.general.discussion/topic6374.aspx Serial port return handling of binary data into array]
*[http://www.di-mgt.com.au/bytearrays.html extensive binary byte array in lieu of string functions handling page]






== CRC CheckSum Algorithm ==




16-bit CRC verification code
== Links for CRC CheckSum Algorithm ==
 
*[http://iatips.com/crc_vb.txt CRC calculation source code in VB using array lookup] - [[ModBus-CRC-Local-Version-routine-v1]]
*[http://www.planet-source-code.com/vb/scripts/ShowCode.asp?txtCodeId=6329&lngWId=10  CRC calculation source code in VB using all calculation] - [[ModBus-CRC-Local-Version-routine-2]]
 
 
== 16-bit CRC verification code Algorithm ==




Only 8 data bits are involved in CRC calculation, with the exclusion of start bit and end bit.
Only 8 data bits are involved in CRC calculation, with the exclusion of start bit and end bit.
Algorithm of CRC code:
Algorithm of CRC code:
*1) Presetting a 16-bit register to hex FFFF (namely 1 for all bits in binary system). The register is called CRC register
*1) Presetting a 16-bit register to hex FFFF. The register is called CRC register


*2) XORing the first 8-bit binary data (the first byte of the communication message frame) with the low 8-bit of 16-bit CRC register,
*2) XORing the first byte of the communication message frame with the low 8-bit of 16-bit CRC register.....then storing the result in CRC register
then storing the result in CRC register


*3) Right-shifting the register data by one bit (towards lower bit) and filling the highest bit with 0, then checking the shift-out bit
*3) Right-shifting the register data by one bit and filling the highest bit with 0, then checking the shift-out bit


*4) If the shift-out bit is 0, repeat step 3 (right-shifting one more bit);
*4) If the shift-out bit is 0, repeat step 3 (right-shifting one more bit);
If the shift-out bit is1, XOR the CRC register data with polynomial A001 (1010 0000 0000 0001)
If the shift-out bit is 1, XOR the CRC register data with polynomial A001 (1010 0000 0000 0001) =  A001


*5) Repeating step 3 and step 4 until all of the 8-bit data have been processed after 8 right-shift operations;
*5) Repeating step 3 and step 4 until all of the 8-bit data have been processed after 8 right-shift operations;
Line 31: Line 37:
*7) When calculation procedures of the first 5 bytes in the communication message frame are completed, the 16-bit CRC verification
*7) When calculation procedures of the first 5 bytes in the communication message frame are completed, the 16-bit CRC verification
code will be generated in the 16-bit CRC register.
code will be generated in the 16-bit CRC register.
== CRC Example Calculations: 1, 06, 40, 03,E8,  18, 22  Hex ==
*1111 1111 1111 1111 CRC
*0000 0000 0000 0001 Data 1
*----------------------------- XOR
*1111 1111 1111 1110 CRC
*0111 1111 1111 1111 CRC 32767      after right shift / shifted bit = 0
*0011 1111 1111  1111 CRC after right shift / shifted bit = 1
*1010 0000 0000  0001 polynomial = A001
*----------------------------- XOR
*1001111111111110 CRC
keep doing till 8 shifts accomplished

Latest revision as of 14:25, 30 July 2008

Comm Port Binary Mode[edit]

Is necessary to use binary mode. Serial port in ASCII mode chokes on null = chr(0) chars



Links for CRC CheckSum Algorithm[edit]


16-bit CRC verification code Algorithm[edit]

Only 8 data bits are involved in CRC calculation, with the exclusion of start bit and end bit. Algorithm of CRC code:

  • 1) Presetting a 16-bit register to hex FFFF. The register is called CRC register
  • 2) XORing the first byte of the communication message frame with the low 8-bit of 16-bit CRC register.....then storing the result in CRC register
  • 3) Right-shifting the register data by one bit and filling the highest bit with 0, then checking the shift-out bit
  • 4) If the shift-out bit is 0, repeat step 3 (right-shifting one more bit);

If the shift-out bit is 1, XOR the CRC register data with polynomial A001 (1010 0000 0000 0001) = A001

  • 5) Repeating step 3 and step 4 until all of the 8-bit data have been processed after 8 right-shift operations;
  • 6) Repeating step 2 to step 5 to process the next byte of the communication message frame;
  • 7) When calculation procedures of the first 5 bytes in the communication message frame are completed, the 16-bit CRC verification

code will be generated in the 16-bit CRC register.


CRC Example Calculations: 1, 06, 40, 03,E8, 18, 22 Hex[edit]

  • 1111 1111 1111 1111 CRC
  • 0000 0000 0000 0001 Data 1
  • ----------------------------- XOR
  • 1111 1111 1111 1110 CRC
  • 0111 1111 1111 1111 CRC 32767 after right shift / shifted bit = 0
  • 0011 1111 1111 1111 CRC after right shift / shifted bit = 1
  • 1010 0000 0000 0001 polynomial = A001
  • ----------------------------- XOR
  • 1001111111111110 CRC

keep doing till 8 shifts accomplished

Retrieved from "http://wiki.amarketplaceofideas.com/index.php?title=CNAOB-Communications-Protocol-Notes&oldid=2577"