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A Data Matrix code is a two-dimensional barcode make up of blocks of black and white modules put together to make either a square or rectangular pattern. The information to be encoded can be text or raw data.
Normally, data size is from a few bytes up to 1,556 bytes. The length of the data depends on the symbol dimension used. To make sure the data can be read even when the pattern is slightly damaged, error correction codes are added which increase symbol strength. A Data Matrix symbol can store up to 2,335 alphanumeric characters. Here is a sample you can scan.
Data Matrix symbols are rectangular in shape and usually square. As more data is added, modules are put together to allow for the data and error correction. Each module can be identified by the "L" shaped black line that runs down the left and across the bottom of each module. In the sample shown above, there are four modules. These "L" shaped sections are known as the "finder pattern". The top and right border of each module are made up of alternating light and dark blocks. Light blocks represent 0 (zero) and the dark blocks represent 1 (one). These are known as the "timing pattern". All of the blocks in the middle of each module make up the data and check codes. The entire pattern can range in size from 8x8 to 144x144 in size.