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`A` : `1000011` b
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`0` : `0110000` b
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`z` : `1111010` b
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`@` : `1000000` b
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`space` : `0100000` b
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In addition, the :term:`ASCII` table also defines several non-printable or control characters. These characters were designed to allow an application to control a printer or a terminal. These control characters include `CR` and `LF`, that are used to terminate a line, and the `BEL` character which causes the terminal to emit a sound.
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`NUL`: `0000000` b
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`BEL`: `0000111` b
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`CR` : `0001101` b
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`LF` : `0001010` b
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`DLE`: `0010000` b
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`STX`: `0000010` b
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`ETX`: `0000011` b
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Some characters are used as markers to delineate the frame boundaries. Many `character stuffing` techniques use the `DLE`, `STX` and `ETX` characters of the ASCII character set. `DLE STX` (resp. `DLE ETX`) is used to mark the beginning (end) of a frame. When transmitting a frame, the sender adds a `DLE` character after each transmitted `DLE` character. This ensures that none of the markers can appear inside the transmitted frame. The receiver detects the frame boundaries and removes the second `DLE` when it receives two consecutive `DLE` characters. For example, to transmit frame `1 2 3 DLE STX 4`, a sender will first send `DLE STX` as a marker, followed by `1 2 3 DLE`. Then, the sender transmits an additional `DLE` character followed by `STX 4` and the `DLE ETX` marker.
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**1** **2** **3** **4**
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`DLE STX` **1** **2** **3** **4** `DLE ETX`
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**1** **2** **3** **DLE** **STX** **4**
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`DLE STX` **1** **2** **3** **DLE** `DLE` **STX** `4` `DLE ETX`
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**DLE STX DLE ETX**
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`DLE STX` **DLE** `DLE` **STX** **DLE** `DLE` ETX** `DLE ETX`
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