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Overview

The barcode adopted by Australia Post is known as the 4-State barcode. It comprises 4 types of bars, each of which is identified by both name and value:

Identifying the 4-state elements of the Barcode

Bars within a barcode are grouped to designate numerical and alphabetical characters. Whilst appearing like a string of individual bars, they are actually sorted into fields.

Each field is allocated a number of grouped bars which can be interpreted by referring to an Encoding Table. The particular configuration of fields, symbols, bars and codes in a barcode are determined by the barcode format.

Start Bars

The first 2 bars in any barcode belong to the Start Bars. These always have the values of ‘1’ and ‘3’ respectively. They ensure that the beginning of a barcode can never be mistaken, even if it is upside down.

Format Control Code

The Format Control Code Field identifies the barcode’s format, which determines the configuration of fields and bars that applies to the whole barcode. This field always occupies bar positions 3 to 6 (inclusive) in every barcode.

The four bars in this field are encoded by the ‘N’ Encoding Table.If the bars have values of ‘0101’, this means the Format Control Code is ‘11’.

The table below shows all the available Format Control Codes, and the type of barcode each code designates.

Sorting Code Field

The Sorting Code Field comprises 16 bars, occupying positions 7 to 22 inclusive in the barcode. These bars are encoded by the "N" Encoding Table, so the 16 bars in this field represent 8 digits.

This 8-digit sorting code represents the Delivery Point Identifier (DPID), which dictates where Australia Post delivers the mail. This can be a letterbox, a PO Box or a rural mail bag. Each address in Australia is allocated a unique DPID.

Customer Information

The Customer Information Field is only available in the barcode formats 2 and 3  and provides the opportunity to include specific information in the barcode.

The field can be either 16 or 31 bars long, depending on the barcode format chosen. These bars can be coded by either ‘C’ or ‘N’ Encoding Tables.

The Customer Information Field is a free format field. Any information can be represented in this field, provided that the information:

• can be coded using one of the two Encoding Tables
• remains within the barcode format bar limit (16 or 31 bars).

If all bars in the field are not required, filler bars (bar value 3) can be used to fill the gap.

Reed Solomon Bars

The Reed Solomon Error Correction Bars ensures that the barcode is resistant to errors or erasures which may be caused by faulty printing, too much reflectance from envelope windows, or factors such as smudging.

There are 12 of these bars, which are located prior to the Stop Bars.

Stop Bars

The last 2 bars in any barcode are the Stop Bars. These have the bar values of ‘1’ and ‘3’ respectively. Like the Start Bars, they ensure that the barcode is read correctly, even if it is read upside down.