SwingeyP
Member
Hello.
I have this code -
If you run it as is and compare the CRC value against this site https://www.lammertbies.nl/comm/info/crc-calculation.html
the CRC will match.
Ok so now comment out all of the 'manual' array loads and un comment the lookup look which loads the array - Surely the same thing - Watch variables are reporting array variables identically.
Like this ...
Run that and compare the CRC - Different answer!
How weird. Is it a bug or am I doing something stupid as usual.
Just noticed that I should have len = len - 1 to bring len back to 4 and the one that took ages to finf was the '0' - I had cut and pasted and of course it's a different character.. - Been a long day sorry.
Regards - Paul
I have this code -
Code:
'$$MØTVU,,,,,,Ø,,,,,,,,, = 0x36f3 (no $$)
Dim data_byte(22) As Byte
Dim data_word As Word
Dim crc As Word
Dim bt As Byte
Dim tmp As Word
Dim i As Byte
Dim len As Byte
Dim polynomial As Word
polynomial = 0x1021 '0x1021 -
Hseropen 9600
len = 4
data_byte(0) = "M" 'M 77 1001101
data_byte(1) = "0"
data_byte(2) = "T"
data_byte(3) = "V"
data_byte(4) = "U"
'data_byte(5) = ","
'data_byte(6) = ","
'data_byte(7) = ","
'data_byte(8) = ","
'data_byte(9) = ","
'data_byte(10) = ","
'For len = 0 To 4 '20
'data_byte(len) = LookUp("MØTVU"), len '$$ will be added for send
'Next len
'-----------------------------------------
'This would be a function
'-----------------------------------------
crc = 0xffff
For i = 0 To len
data_word = data_byte(i)
data_word = ShiftLeft(data_word, 8) 'shift the data left 8
crc = crc Xor data_word 'XOR the data with the CRC
For bt = 0 To 7
tmp = crc And 0x8000 'and the CRC with 0x8000
If tmp <> 0 Then 'if this vale <> 0 then will be either 8000 or 0
crc = ShiftLeft(crc, 1) 'shift the CRC left 1
crc = crc Xor polynomial 'XOR the CRC with polynomial
Else
crc = ShiftLeft(crc, 1) 'else just shift the crc left 1
Endif
Next bt
Next i
Hserout "CRC = ", #crc, CrLf 'M = 0x7899 - or maybe 0x55f5 -
End
'M = 30873 - 0x7899
'M0 = 20684 - 0x50CC
'M0T = 35972 - 0x8C84
'M0TV = 60983 - 0xee37
'M0TVU = 8624 - ox21b0
'0123456789 = 0x7d61If you run it as is and compare the CRC value against this site https://www.lammertbies.nl/comm/info/crc-calculation.html
the CRC will match.
Ok so now comment out all of the 'manual' array loads and un comment the lookup look which loads the array - Surely the same thing - Watch variables are reporting array variables identically.
Like this ...
Code:
'$$MØTVU,,,,,,Ø,,,,,,,,, = 0x36f3 (no $$)
Dim data_byte(22) As Byte
Dim data_word As Word
Dim crc As Word
Dim bt As Byte
Dim tmp As Word
Dim i As Byte
Dim len As Byte
Dim polynomial As Word
polynomial = 0x1021 '0x1021 -
Hseropen 9600
'len = 4
'data_byte(0) = "M" 'M 77 1001101
'data_byte(1) = "0"
'data_byte(2) = "T"
'data_byte(3) = "V"
'data_byte(4) = "U"
'data_byte(5) = ","
'data_byte(6) = ","
'data_byte(7) = ","
'data_byte(8) = ","
'data_byte(9) = ","
'data_byte(10) = ","
For len = 0 To 4 '20
data_byte(len) = LookUp("MØTVU"), len '$$ will be added for send
Next len
'-----------------------------------------
'This would be a function
'-----------------------------------------
crc = 0xffff
For i = 0 To len
data_word = data_byte(i)
data_word = ShiftLeft(data_word, 8) 'shift the data left 8
crc = crc Xor data_word 'XOR the data with the CRC
For bt = 0 To 7
tmp = crc And 0x8000 'and the CRC with 0x8000
If tmp <> 0 Then 'if this vale <> 0 then will be either 8000 or 0
crc = ShiftLeft(crc, 1) 'shift the CRC left 1
crc = crc Xor polynomial 'XOR the CRC with polynomial
Else
crc = ShiftLeft(crc, 1) 'else just shift the crc left 1
Endif
Next bt
Next i
Hserout "CRC = ", #crc, CrLf 'M = 0x7899 - or maybe 0x55f5 -
End
'M = 30873 - 0x7899
'M0 = 20684 - 0x50CC
'M0T = 35972 - 0x8C84
'M0TV = 60983 - 0xee37
'M0TVU = 8624 - ox21b0
'0123456789 = 0x7d61How weird. Is it a bug or am I doing something stupid as usual.
Just noticed that I should have len = len - 1 to bring len back to 4 and the one that took ages to finf was the '0' - I had cut and pasted and of course it's a different character.. - Been a long day sorry.
Regards - Paul
Last edited: