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CRC 16 in SCL language

Created by: giorgiofacco at: 4/8/2010 11:26 AM (24 Replies)

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4/8/2010 11:26 AM	Rate (0)
giorgiofacco Posts: 22 Rating: (0)	Hi, someone realized a CRC16 algorithm in SCL language? Can help me? Thank you Best regards Giorgio Facco
giorgiofacco Posts: 22 Rating: (0)
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4/8/2010 2:02 PM	Rate (1)
Aret Posts: 2348 Rating: (265)	Google says (Delphi) procedure CRC16 (cnt: integer; DATA: ShortString); var i,j: Integer; crc: Integer; CRC_POLYNOM: Integer; begin CRC_POLYNOM := $1021; for i := 0 to cnt do (* cnt = number of protocol bytes without CRC *) begin crc := crc xor integer (DATA[i]); for j := 0 to 8 do begin if ((crc or $0001)<>0) then crc := (crc shr 1) xor CRC_POLYNOM else crc := (crc shr 1); end; end; end; Now i guess you can transform it to SCL
Aret Posts: 2348 Rating: (265)
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4/8/2010 2:29 PM	Rate (0)
giorgiofacco Posts: 22 Rating: (0)	thank you. Is it Pascal language? Best regards Giorgio Facco
giorgiofacco Posts: 22 Rating: (0)
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4/9/2010 7:09 AM	Rate (0)
Aret Posts: 2348 Rating: (265)	Almost:^) Delphi
Aret Posts: 2348 Rating: (265)
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4/13/2010 7:11 PM	Rate (7)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 11/20/2025 Posts: 1561 Rating: (540)	The best way is to use a lookup table. The following is for a modbus CRC-16 (polynomial = 16#8001). Add the following to the VAR (static) section of your code. [code] // CRC lookup tables. Ideally the initialisation would be performed in one ARRAY. // However, SCL limits the static initialisation to a maximum of 255 elements, // which is a shame, as we need to initialise 256 elements. Doh! // The solution is to have 2 initialisers of 128 elements and then combine them // during runtime initialisation (by simply copying the elements across to another // array of the correct size). CRCLoTable1 : ARRAY [0..127] OF BYTE := 0, 192, 193, 1, 195, 3, 2, 194, 198, 6, 7, 199, 5, 197, 196, 4, 204, 12, 13, 205, 15, 207, 206, 14, 10, 202, 203, 11, 201, 9, 8, 200, 216, 24, 25, 217, 27, 219, 218, 26, 30, 222, 223, 31, 221, 29, 28, 220, 20, 212, 213, 21, 215, 23, 22, 214, 210, 18, 19, 211, 17, 209, 208, 16, 240, 48, 49, 241, 51, 243, 242, 50, 54, 246, 247, 55, 245, 53, 52, 244, 60, 252, 253, 61, 255, 63, 62, 254, 250, 58, 59, 251, 57, 249, 248, 56, 40, 232, 233, 41, 235, 43, 42, 234, 238, 46, 47, 239, 45, 237, 236, 44, 228, 36, 37, 229, 39, 231, 230, 38, 34, 226, 227, 35, 225, 33, 32, 224; CRCLoTable2 : ARRAY [0..127] OF BYTE := 160, 96, 97, 161, 99, 163, 162, 98, 102, 166, 167, 103, 165, 101, 100, 164, 108, 172, 173, 109, 175, 111, 110, 174, 170, 106, 107, 171, 105, 169, 168, 104, 120, 184, 185, 121, 187, 123, 122, 186, 190, 126, 127, 191, 125, 189, 188, 124, 180, 116, 117, 181, 119, 183, 182, 118, 114, 178, 179, 115, 177, 113, 112, 176, 80, 144, 145, 81, 147, 83, 82, 146, 150, 86, 87, 151, 85, 149, 148, 84, 156, 92, 93, 157, 95, 159, 158, 94, 90, 154, 155, 91, 153, 89, 88, 152, 136, 72, 73, 137, 75, 139, 138, 74, 78, 142, 143, 79, 141, 77, 76, 140, 68, 132, 133, 69, 135, 71, 70, 134, 130, 66, 67, 131, 65, 129, 128, 64; CRCHiTable1 : ARRAY [0..127] OF BYTE := 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65; CRCHiTable2 : ARRAY [0..127] OF BYTE := 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64, 0, 193, 129, 64, 1, 192, 128, 65, 0, 193, 129, 64, 1, 192, 128, 65, 1, 192, 128, 65, 0, 193, 129, 64; // Actual CRC lookup tables used in code, data from above initialisers copied into this at runtime CRCLoTable : ARRAY [0..255] OF BYTE; CRCHiTable : ARRAY [0..255] OF BYTE; CRCHi : BYTE; // Calculated CRC MSB CRCLo : BYTE; // Calculated CRC LSB CRCPtr : INT; // Calculated CRC data pointer CRCIndex : INT; // Calculated CRC index into CRC lookup tables [/code] Then in the initialisation section of your code (OB100 / OB102). [code] // Copy over the CRC lookup table data from static initialiser arrays to the actual lookup table arrays FOR i := 0 TO 127 DO CRCLoTable[i] := CRCLoTable1[i]; CRCLoTable[i + 128] := CRCLoTable2[i]; CRCHiTable[i] := CRCHiTable1[i]; CRCHiTable[i + 128] := CRCHiTable2[i]; END_FOR; [/code] The CRC is then calculated as follows (where PacketLength is the length of your data packet and TXBuf is the byte array buffer containing your data. [code] CRCHi := 16#FF; // Initialise the CRC's CRCLo := 16#FF; CRCPtr := 1; // The CRC start byte WHILE CRCPtr <= PacketLength DO // While all data packet bytes not processed CRCIndex := BYTE_TO_INT(CRCHi XOR TXBuf[CRCPtr]); // Calulate the lookup table index CRCHi := CRCLo XOR CRCHiTable[CRCIndex]; // Get actual CRC MSB from lookup table CRCLo := CRCLoTable[CRCIndex]; // Get actual CRC LSB from lookup table CRCPtr := CRCPtr + 1; // Next data byte END_WHILE; [/code] CRCLo and CRCHi will then contain the CRC LSB and CRC MSB of the data.
	Last edited by: smiffy at: 2/13/2018 5:52:18 PM Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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This contribution was helpful to 2 thankful Users NoviceCLX MartijnD

5/5/2010 11:00 AM	Rate (0)
giorgiofacco Posts: 22 Rating: (0)	Thank you ! I 'll test. Best regards Giorgio Facco
giorgiofacco Posts: 22 Rating: (0)
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5/18/2010 9:30 AM	Rate (0)
giorgiofacco Posts: 22 Rating: (0)	Hi, both solutions works!! tank you for the help Giorgio Facco
giorgiofacco Posts: 22 Rating: (0)
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This contribution was helpful to 1 thankful Users S_Moderator

5/18/2010 2:28 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 11/20/2025 Posts: 1561 Rating: (540)	The lookup table will use considerably less CPU time as a lot of the work has been done already in the table data. The only drawback is that you will need to use a bit more program memory to store the table data. It is a trade off between CPU time and memory, between the 2 methods. Table - Low CPU time but more program memory required. Calculaton from scratch - More CPU time but less program memory required. Generally in todays modern PLC's, memory is a lot cheaper to buy than CPU time. So it makes sense to use the table method. The choice is yours.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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5/24/2010 6:24 PM	Rate (0)
Amoralis Posts: 46 Rating: (5)	Hello! Why do You need it in SCL? For me, it's better to make such things more effectively (SCL generates a lot of useless code). Please look at /tf/WW/en/Posts/1889 there is good AWL sources.
Amoralis Posts: 46 Rating: (5)
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9/18/2017 2:03 PM	Rate (0)
Elonen Bronze Member Joined: 4/11/2012 Last visit: 10/31/2025 Posts: 181 Rating: (34)	Aret Google says (Delphi) procedure CRC16 (cnt: integer; DATA: ShortString); var i,j: Integer; crc: Integer; CRC_POLYNOM: Integer; begin CRC_POLYNOM := $1021; for i := 0 to cnt do (* cnt = number of protocol bytes without CRC ) begin crc := crc xor integer (DATA[i]); for j := 0 to 8 do* begin if ((crc or $0001)<>0) then crc := (crc shr 1) xor CRC_POLYNOM else crc := (crc shr 1); end; end; end; Quick question: Why is it for j:= 0 to 8? Won't that make 9 repetitions? Is this normal for this particular CRC type, and other CRC types go with 8 repetitions (1 to 8)? Edit: I'm going with the calculation heavy CRC solution as it's easier to document but I seem to find conflicting methods for implementing the CRC calculation, hoping this will clarify it for me.
	Last edited by: Elonen at: 9/18/2017 2:05:23 PM
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