INFICON PSG55x ATM to Medium Vacuum Gauge (RS232C / RS485C) - Manual (Page 10)

10
tira59e1 (2010-07) RS232C.cp
The data packages are secured with CRC16 in Little Endian.
CRC polynominal 0x8408
CRC initial value 0xFFFF
To illustrate how the checksum can be calculated and verified, an example of a
code is given below:
using System;
class Program
{
static void Main()
{
// the following test array is a valid pcg5xx frame with crc16 at the end
byte [] arr = new byte [] { 0x00, 0x00, 0x00, 0x05, 0x01, 0x00, 0xDD, 0x00, 0x00, 0xAB, 0x21};
UInt16 crc;
Boolean b;
// Calculate the crc of the test array arr, of course without crc (therefore length minus 2)
crc = Crc16 .Create(arr, ( Byte )(arr.Length - 2));
// Check, if the test array has a correct crc at the end (it is correct, therefore the returnvalue is
true)
b = Crc16 .Check(arr, ( Byte )arr.Length);
}
}
public class Crc16
{
// initial value for crc16
public static UInt16 inital = 0xFFFF;
// function to create a crc16
public static UInt16 Create( Byte [] buffer, Byte length)
{
UInt16 crc16 = new UInt16 ();
UInt16 i = 0;
// Initial Value for CRC calculation
crc16 = Crc16 .inital;
while (i < length)
{
crc16 = (
UInt16 )(( Crc16 .crc16Tab[(crc16 ^ buffer[i++]) & ( Byte )0xFF]) ^ (crc16 >> 8));
}
return crc16;
}
// function to check a buffer with a crc16 at the end
public static Boolean Check( Byte [] buffer, Byte length)
{
UInt16 crc16 = Crc16 .inital;
UInt16 i = 0;
// calculate crc for the buffer without crc
while (i < length)
{
crc16 = (
UInt16 )(( Crc16 .crc16Tab[(crc16 ^ buffer[i++]) & ( Byte )0xFF]) ^ (crc16 >> 8));
}
if (crc16 == 0)
{
return true ;
}
return false ;
}
// crc array
public static UInt16 [] crc16Tab =
{
0x0000, 0x1189, 0x2312, 0x329B, 0x4624, 0x57AD, 0x6536, 0x74BF,
0x8C48, 0x9DC1, 0xAF5A, 0xBED3, 0xCA6C, 0xDBE5, 0xE97E, 0xF8F7,
0x1081, 0x0108, 0x3393, 0x221A, 0x56A5, 0x472C, 0x75B7, 0x643E,
0x9CC9, 0x8D40, 0xBFDB, 0xAE52, 0xDAED, 0xCB64, 0xF9FF, 0xE876,
0x2102, 0x308B, 0x0210, 0x1399, 0x6726, 0x76AF, 0x4434, 0x55BD,
0xAD4A, 0xBCC3, 0x8E58, 0x9FD1, 0xEB6E, 0xFAE7, 0xC87C, 0xD9F5,
0x3183, 0x200A, 0x1291, 0x0318, 0x77A7, 0x662E, 0x54B5, 0x453C,
0xBDCB, 0xAC42, 0x9ED9, 0x8F50, 0xFBEF, 0xEA66, 0xD8FD, 0xC974,
0x4204, 0x538D, 0x6116, 0x709F, 0x0420, 0x15A9, 0x2732, 0x36BB,
0xCE4C, 0xDFC5, 0xED5E, 0xFCD7, 0x8868, 0x99E1, 0xAB7A, 0xBAF3,
0x5285, 0x430C, 0x7197, 0x601E, 0x14A1, 0x0528, 0x37B3, 0x263A,
0xDECD, 0xCF44, 0xFDDF, 0xEC56, 0x98E9, 0x8960, 0xBBFB, 0xAA72,
Calculating CRC
CRC Example Code