Biphase mark code: Difference between revisions
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#REDIRECT [[Differential Manchester encoding]] |
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The '''Biphase Mark Code''' is a type of encoding for binary data streams. |
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If a binary data stream is sent without any modification via any channel, |
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if there are long series of logical ones or zeros without any change, this |
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can cause problems in synchronization. Streams encoded in [[NRZ]] are affected |
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by the same problem. |
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Using Biphase Mark Code makes synchronization easier. |
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[[de:Biphase-Mark-Code]] |
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When encoding, |
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[[it:Biphase Mark Code]] |
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the [[frequency]] of the [[clock]] is twice the |
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[[bitrate]] of the original signal. Every bit of the original data is represented as |
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two logical states which, together, form a cell. Every logical 1 is represented |
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as a couple of two different bits (10 or 01). The logical 0 is represented as |
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two equal bits (00 or 11). Every logical level at the start of a cell is inverted |
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to the level at the end of the previous cell. |
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In BMC coding the logical 1 and 0 are represented with the same voltage, using a |
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different polarity. It is shown in the following image: |
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[[Image:Bmc.png|600px|center|none]] |
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BMC coding provides a better synchronization since there is a change in the polarity |
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at least every two bits. It is not necessary to know the polarity of the sent signal |
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since the information is not kept in the actual values of the |
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voltage but in their change: in other words it does not matter whether a logical 1 or |
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0 is received, but only whether the polarity is the same or is different from the previous |
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value; this makes synchronization even easier. |
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Finally, BMC coded signals have null mean value, thus reducing the necessary transmitting |
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power. |
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All these good points are achieved at the expense of doubling clock frequency. |
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Latest revision as of 12:06, 26 December 2016
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