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attributes of the bar code, such as height and width, can be set
using other commands.
The set bar code height command (GS h) specifies the height of
the bar code in dots, or 1/8
th
mm. The maximum height for a bar
code is 256 dots, or 32mm. In cases where a taller bar code is
needed, a second bar code can be printed below the first at the
same left offset.
The set bar code module width (GS w) and set bar code element
width (GS W) commands can be used to alter the width of the bar
code. See the command descriptions later in the next chapter for a
full explanation of the differences between these two commands.
The POSTNET bar code symbology is an exception and does not
respond to any of these commands. Instead, it always prints
within the U.S. Postal Service’s specifications.
The limitations of each symbology must be adhered to when
sending data for a bar code. For example, you should not send
alphabetic characters to symbologies that only accept numeric
data (like the UPC/EAN symbology).
Other items must also be considered when printing bar codes.
You must leave sufficient blank space on either side of the bar
code to create a quiet zone. You must also select a good
ratio/element size if the default values are not being used, and you
must allow adequate room for the bar code to be printed on the
label. If you ignore any of these items, the bar code that is printed
may be unreadable.
A bar code object is self-terminating and will be processed as
soon as the proper amount of data has been sent to it. The print
bar code command’s (GS k) second parameter specifies whether a
fixed amount of data will be sent or whether delimiters will be
used. In either case, the data sent must match the parameter
setting. If a fixed number of characters are specified, then the
exact number of characters specified must be sent. If delimiters
are indicated, then matching characters must be sent before and
after the bar code data to specify the beginning and end of the
data. If an incorrect number of characters or delimiters are sent,
the LabelWriter will not print correctly.
