Así es como lo hago:
La columna A es el texto que quiero codificar.
La columna B es una fórmula para envolver ese texto en asteriscos (que es lo que, para mí, califica la entrada como texto): =CONCATENATE("*",A2,"*")
El texto de la columna B está formateado con la fuente del código de barras, con el tamaño ajustado para su legibilidad, impresión y escaneo.
Espero que esto ayude de alguna manera.
ADDENDUM
Encontré el siguiente macro , cuyo autor es Eric Townsend Schmidt. Todo el mérito es suyo.
Public Function code128$(chaine$)
'This function is governed by the GNU Lesser General Public License (GNU LGPL)
'V 2.0.0
'Parameters : a string
'Return : * a string which give the bar code when it is dispayed with CODE128.TTF font
' * an empty string if the supplied parameter is no good
Dim i%, checksum&, mini%, dummy%, tableB As Boolean
code128$ = ""
If Len(chaine$) > 0 Then
'Check for valid characters
For i% = 1 To Len(chaine$)
Select Case Asc(Mid$(chaine$, i%, 1))
Case 32 To 126, 203
Case Else
i% = 0
Exit For
End Select
Next
'Calculation of the code string with optimized use of tables B and C
code128$ = ""
tableB = True
If i% > 0 Then
i% = 1 'i% devient l'index sur la chaine / i% become the string index
Do While i% <= Len(chaine$)
If tableB Then
'See if interesting to switch to table C
'yes for 4 digits at start or end, else if 6 digits
mini% = IIf(i% = 1 Or i% + 3 = Len(chaine$), 4, 6)
GoSub testnum
If mini% < 0 Then 'Choice of table C
If i% = 1 Then 'Starting with table C
code128$ = Chr$(205)
Else 'Switch to table C
code128$ = code128$ & Chr$(199)
End If
tableB = False
Else
If i% = 1 Then code128$ = Chr$(204) 'Starting with table B
End If
End If
If Not tableB Then
'We are on table C, try to process 2 digits
mini% = 2
GoSub testnum
If mini% < 0 Then 'OK for 2 digits, process it
dummy% = Val(Mid$(chaine$, i%, 2))
dummy% = IIf(dummy% < 95, dummy% + 32, dummy% + 100)
code128$ = code128$ & Chr$(dummy%)
i% = i% + 2
Else 'We haven't 2 digits, switch to table B
code128$ = code128$ & Chr$(200)
tableB = True
End If
End If
If tableB Then
'Process 1 digit with table B
code128$ = code128$ & Mid$(chaine$, i%, 1)
i% = i% + 1
End If
Loop
'Calculation of the checksum
For i% = 1 To Len(code128$)
dummy% = Asc(Mid$(code128$, i%, 1))
dummy% = IIf(dummy% < 127, dummy% - 32, dummy% - 100)
If i% = 1 Then checksum& = dummy%
checksum& = (checksum& + (i% - 1) * dummy%) Mod 103
Next
'Calculation of the checksum ASCII code
checksum& = IIf(checksum& < 95, checksum& + 32, checksum& + 100)
'Add the checksum and the STOP
code128$ = code128$ & Chr$(checksum&) & Chr$(206)
End If
End If
Exit Function
testnum:
'if the mini% characters from i% are numeric, then mini%=0
mini% = mini% - 1
If i% + mini% <= Len(chaine$) Then
Do While mini% >= 0
If Asc(Mid$(chaine$, i% + mini%, 1)) < 48 Or Asc(Mid$(chaine$, i% + mini%, 1)) > 57 Then Exit Do
mini% = mini% - 1
Loop
End If
Return
End Function