Public Sub checksum(field As String)
   If field = "21" Then
      CS = "*"
        CS = 0
        For i = 1 To Len(field)
           CS = CS Xor Asc(Mid$(field, i, 1))
           Next
           CS = Hex(CS)
           If Len(CS) = 1 Then
           CS = "0" & CS
           CS = "*" & CS
End Sub
这个函数的算法具体是怎样的啊,我不大明白.

假如不考虑代码的错误,大哥能否告诉我这段代码的具体实现的算法功能?

是将字符串参数转成ASCII再异或嘛?和谁异或?