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crc16.py
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#* File: CRC16.PY
#* CRC-16 (reverse) table lookup for Modbus or DF1
#*
# Source: http://www.digi.com/wiki/developer/index.php/Python_CRC16_Modbus_DF1
INITIAL_MODBUS = 0xFFFF
INITIAL_DF1 = 0x0000
table = (
0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,
0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,
0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,
0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,
0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,
0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,
0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,
0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,
0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,
0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,
0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,
0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,
0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,
0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,
0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,
0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,
0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,
0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,
0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,
0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,
0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,
0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,
0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,
0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,
0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,
0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,
0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,
0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,
0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,
0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,
0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,
0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040 )
def calcByte( ch, crc):
"""Given a new Byte and previous CRC, Calc a new CRC-16"""
if type(ch) == type("c"):
by = ord( ch)
else:
by = ch
crc = (crc >> 8) ^ table[(crc ^ by) & 0xFF]
return (crc & 0xFFFF)
def calcString( st, crc):
"""Given a bunary string and starting CRC, Calc a final CRC-16 """
for ch in st:
crc = (crc >> 8) ^ table[(crc ^ ord(ch)) & 0xFF]
return crc
if __name__ == '__main__':
# test Modbus
print "testing Modbus messages with crc16.py"
print "test case #1:",
crc = INITIAL_MODBUS
st = "\xEA\x03\x00\x00\x00\x64"
for ch in st:
crc = calcByte( ch, crc)
if crc != 0x3A53:
print "BAD - ERROR - FAILED!",
print "expect:0x3A53 but saw 0x%x" % crc
else:
print "Ok"
print "test case #2:",
st = "\x4b\x03\x00\x2c\x00\x37"
crc = calcString( st, INITIAL_MODBUS)
if crc != 0xbfcb:
print "BAD - ERROR - FAILED! ",
print "expect:0xBFCB but saw 0x%x" % crc
else:
print "Ok"
print "test case #3:",
st = "\x0d\x01\x00\x62\x00\x33"
crc = calcString( st, INITIAL_MODBUS)
if crc != 0x0ddd:
print "BAD - ERROR - FAILED!",
print "expect:0x0DDD but saw 0x%x" % crc
else:
print "Ok"
print
print "testing DF1 messages with crc16.py"
print "test case #1:",
st = "\x07\x11\x41\x00\x53\xB9\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
# DF1 uses same algorithm - just starts with CRC=0x0000 instead of 0xFFFF
# note: <DLE><STX> and the <DLE> of the <DLE><ETX> pair NOT to be included
crc = calcString( st, INITIAL_DF1)
crc = calcByte( "\x03", crc) # final ETX added
if crc != 0x4C6B:
print "BAD - ERROR - FAILED!",
print "expect:0x4C6B but saw 0x%x" % crc
else:
print "Ok"
# end file