Mark and space

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Short description: States of a communications signal

Mark and space are terms used in telecommunications to describe two different signal states of a communications signal, generally at the physical layer of a communications system. The terms derive from the early days of the electric telegraph system, where the marking state would cause a mark to be output on paper, and the spacing state would create no mark.

7-bit Asynchronous Data Communication surrounded by start, parity and end elements including one "0" (spacing) start element and one "1" (marking) stop element[1]
Diagram of RS-232 signalling for an uppercase ASCII "K" character (0x4b) with 1 start bit, 8 data bits, 1 stop bit. Mark and Space depict negative and positive voltage levels.

The terms would continue to be used in systems such as RS-232, with similar conventions, that "mark" would be encoded by a negative voltage (or current flow), and "space" by a positive voltage (or no current flow).[2] In such systems, the line is typically left in the "mark" state when idle.[3]

"Mark" is generally identified with the binary digit "1" and "space" with the binary digit "0".[2]

References

  1. ↑ MIL-STD-188-100, Pg. B-8, Fig. 3, 1972.
  2. ↑ 2.0 2.1 Freeman, Roger L. (2004-06-11) (in en). Telecommunication System Engineering. John Wiley & Sons. ISBN 978-0-471-45133-4. https://books.google.com/books?id=K4ribVEOhSAC&dq=mark+and+space+binary&pg=PA366. 
  3. ↑ Martin, James; Martin, James Thomas; S.J, James Martin (1976) (in en). Telecommunications and the Computer. Prentice Hall Professional. ISBN 978-0-13-902494-8. https://books.google.com/books?id=UE0gcFERpisC&dq=mark+and+space+ccitt&pg=PA54. 

See also




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