X21 » History » Version 1
laforge, 01/15/2023 06:03 PM
| 1 | 1 | laforge | h1. X.21 |
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| 3 | X.21 is a specification for a differential, serial interface introduced in the mid-1970 by ITU-T. |
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| 5 | It was used as a digital signaling interface between (typically customer-owned) [[DTE]] and (typically provider-owned) [[DCE]]. |
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| 7 | X.21 was primarily used in the [[CSPDN__Datex-L|CSPDN]] networks such as DATEX-L. |
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| 9 | h2. Types of Signals |
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| 11 | Note: Each of those signals actually has two physical circuits as the signals are all differential. |
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| 13 | |_.Name|_.Direction|_.Description| |
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| 14 | |Transmit Data|DTE -> DCE|Data transmitted by the DTE| |
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| 15 | |Control|DTE -> DCE|Indicates the meaning of the data sent on _Transmit Data_| |
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| 16 | |Receive Data|DTE <- DCE|Data received by the DTE| |
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| 17 | |Indication|DTE <- DCE|Indicates the type of data received on _Receive Data_| |
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| 18 | |Signal Element Timing|DTE <- DCE|The bit-clock| |
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| 19 | |Byte Timing|DTE <- DCE|The byte-clock (optional)| |
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| 21 | h2. External Links |
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| 23 | * https://en.wikipedia.org/wiki/X.21 |
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| 24 | * http://www.arcelect.com/X21_interface.htm |
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| 25 | * http://old.pinouts.ru/SerialPorts/x21_pinout.shtml |
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| 26 | * https://www.itu.int/rec/T-REC-X.21/recommendation.asp?lang=en&parent=T-REC-X.21-199209-I |
