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'=================================
'名称 CRC16
'参数 Data Byte() 数据内容
' Length Integer 计算长度,默认值 1
'返回 Byte()
'类型 Private Function
'说明 计算CRC16值
'日期 2007-03-09
' 2007-03-15 修改Length判断
'=================================
Private Function CRC16(Data() As Byte, Optional ByVal Offset As Integer = 0, Optional ByVal Length As Integer = 0) As Byte()
Dim CRC16Lo As Byte, CRC16Hi As Byte 'CRC寄存器
Dim CL As Byte, CH As Byte '多项式码&HA001
Dim SaveHi As Byte, SaveLo As Byte
Dim I As Integer
Dim Flag As Integer
Dim ReturnData(1) As Byte
CRC16Lo = &HFF
CRC16Hi = &HFF
CL = &H1
CH = &HA0
Length = IIf(Length < 1, UBound(Data) - Offset, Length - 1) 'Update 2007-03-15
For I = Offset To Offset + Length
CRC16Lo = CRC16Lo Xor Data(I) '每一个数据与CRC寄存器进行异或
For Flag = 0 To 7
SaveHi = CRC16Hi
SaveLo = CRC16Lo
CRC16Hi = CRC16Hi \ 2 '高位右移一位
CRC16Lo = CRC16Lo \ 2 '低位右移一位
If ((SaveHi And &H1) = &H1) Then '如果高位字节最后一位为1
CRC16Lo = CRC16Lo Or &H80 '则低位字节右移后前面补1
End If '否则自动补0
If ((SaveLo And &H1) = &H1) Then '如果LSB为1,则与多项式码进行异或
CRC16Hi = CRC16Hi Xor CH
CRC16Lo = CRC16Lo Xor CL
End If
Next
Next
ReturnData(0) = CRC16Lo 'CRC低位
ReturnData(1) = CRC16Hi 'CRC高位
CRC16 = ReturnData
End Function