' This VBA macro works in Excel; it will not work in
' Google Sheets, OpenOffice, or GNumeric.

' Insert the following into an empty new Excel spreadsheet and
' paste the following two macros. Then run the two that begin with
' the word "Action"

Sub Action_CreateCharTable()

    HexDigits = "0123456789ABCDEF"
    
    ' Fill in values from 00 to FF
    For Column = 1 To 16
        For Row = 1 To 16
            CellName = Chr(Column + 64) & Row
            HexValue = "'" & Mid(HexDigits, Row, 1) & Mid(HexDigits, Column, 1)
            Range(CellName).Value = HexValue
        Next
    Next

    ' Align values in the center of each cell
    Range("A1:P16").Select
    With Selection
        .HorizontalAlignment = xlCenter
        .VerticalAlignment = xlBottom
        .WrapText = False
        .Orientation = 0
        .AddIndent = False
        .IndentLevel = 0
        .ShrinkToFit = False
        .ReadingOrder = xlContext
        .MergeCells = False
    End With

    Range("A1").Select

End Sub

Sub Action_SaveFile()

    ' Collect hexadecimal numbers from cells into a string
    HexString = ""
    For Row = 1 To 16
        For Column = 1 To 16
            CellName = Chr(Column + 64) & Row
            HexString = HexString & Range(CellName).Value
        Next
    Next
    
    Call CreateHexFile("ASCII.BIN", HexString)
End Sub

' USAGE: Call CreateHexFile(FileName, StringContent)
Sub CreateHexFile(FileName, Content)

    ' Create the file
    Set FSO = CreateObject("Scripting.FileSystemObject")
    Set F = FSO.CreateTextFile(FileName, 1, 0)
    
    If VarType(Content) = vbString Then
        D = 0         ' Number of hexadecimal digits we have encountered
        Output = ""   ' Binary string output
        For I = 1 To Len(Content)
            ' The following line captures digits and uppercase and lowercase letters (A-F) and
            ' outputs a number between 0 and 16. If it's zero, then that means
            ' the input character was not a hexadecimal digit.
            P = InStr("123456789abcdef0123456789ABCDEF", Mid(Content, I, 1))
            If P > 0 Then
                D = D + 1
                P = P And 15
                If D And 1 Then
                    ' Store high nibble in U
                    U = P * 16
                Else
                    ' Combine high nibble and low nibble U + P
                    Output = Output & Chr(U + P)
                End If
            End If
        Next
        ' Write last digit if there were an odd number of digits:
        If D And 1 Then Output = Output & Chr(U)
        F.Write Output
    End If
    
    F.Close

End Sub