The expression data bit describes the broadcasting of the real information content. This information can be coded in symbols (sometimes referred as chips) that are, then, physically transmitted from sender to receiver. The receiver has to decode the symbols back into data bits to access the information. The symbol rate is, therefore, always greater than or equal to the bit rate.
The ATA8210/15 supports two coding modes:
Manchester coding – Implements two symbols per data bit
Non-return-to-zero (NRZ) coding – Implemented in a straightforward manner, one bit is represented by one symbol.
There is always a transition between the two symbols of one data bit so that one data bit always consists of a ‘0’ and a ‘1’. The polarity can be either way; see the following figure.Figure 3-3. Manchester Code
Manchester coding has many advantages, such as simple clock recovery, no DC component and error detection by code violation. The drawbacks are coding/decoding effort and the increased symbol rate, which is twice the data rate.
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