Grass Valley XSwitch Feb 08 2006 - Manual (Page 37)

XSWITCH Installation and Operation Manual 37
Calculating the CRC
Calculating the CRC
Given : The XSWITCH information for the fields:
and the basic program to calculate the CRC:
BASIC CRC PROGRAM VER. 2.0 USING VISUAL BASIC 3.0
Static P(200) As integer
ICRC = 0
POLY = &H8408
Dstring$ = Input_Text$ This is the input string.
D = 0
i = 1
P(0) = 0
For J = 1 To Len (Dstring$)
c$ = Mid$(Dstring$,J,1)
Casc = Asc (c$) ‘Finds decimal value contained in ch-
arcter’s ASCII value.
D = D * 16 + Casc ‘Hex value calculated.
P(0) = P(0) + 1
P(i) = D
i = i + 1
D = 0
Next J
‘After calculating input string’s characters to hex val-
ue,
CRC = ICRC Calculate the CRC.
i = 1 to P(0)
D = P(i)
For J = 1 To 8
XFLG = (CRC Xor D) And 1
CRC = Int(CRC/2) And &H7FFF
If XFLG Then CRC = CRC Xor POLY
D = Int (D / 2)
Next J
Next i
................CrCHexValue$ = Hex$(CRC) ‘This is EN-
TIRE CRC string.
dummylength = Len(CrCHexValue$)
LSB = Val (“&H” + Right$(CrCHexValue$, 2)) ‘Convert
hex value to decimal value.
MSB = 0
If dummylength = 3 Then MSB = Val(“&H” + Left$
(CrCHexValue$, 1))
If dummylength > 3 Then MSB = Val(“&H” + Mid$ (CrCHex-
DEST SRC LEN C/C DATA1 ... DATAn CRCL CRCH