Difference between revisions of "Serial line"
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| − | A '''serial line''' is a means of transmitting data in [[bit]] serial fashion, often over a [[communication link]] such as a telephone line. There are two principal forms: | + | A '''serial line''' is a means of transmitting data in [[bit]] [[serial]] fashion, often over a [[communication link]] such as a telephone line. There are two principal forms: |
* [[asynchronous serial line]]s, in which the format is self-[[clock]]ing (i.e. the start location of each character can be inferred from the data stream), and | * [[asynchronous serial line]]s, in which the format is self-[[clock]]ing (i.e. the start location of each character can be inferred from the data stream), and | ||
* [[synchronous serial line]]s, where each character starts immediately after the previous one, and is therefore not self-clocking | * [[synchronous serial line]]s, where each character starts immediately after the previous one, and is therefore not self-clocking | ||
| − | Both serial line [[protocol]]s requires two signal levels: idle (mark, high), and asserted (space, low). (The polarity is a legacy from telegraphy, where the line was held high in order to show that the line was not broken, and that the transmitter was functional.) | + | Both serial line [[protocol]]s requires two signal levels: '''idle''' ('''mark''', high [[voltage]]), and '''asserted''' ('''space''', low voltage). (The polarity is a legacy from telegraphy, where the line was held high in order to show that the line was not broken, and that the transmitter was functional.) |
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| + | If the line is held in the 'asserted' state for longer than a character time, this is called a '''break''' condition, and it can be detected by the receiver and signalled to the user specially. This is often used to [[interrupt]] the computer on the other end of the line. | ||
{{semi-stub}} | {{semi-stub}} | ||
[[Category: Communication Basics]] | [[Category: Communication Basics]] | ||
Revision as of 15:30, 5 August 2021
A serial line is a means of transmitting data in bit serial fashion, often over a communication link such as a telephone line. There are two principal forms:
- asynchronous serial lines, in which the format is self-clocking (i.e. the start location of each character can be inferred from the data stream), and
- synchronous serial lines, where each character starts immediately after the previous one, and is therefore not self-clocking
Both serial line protocols requires two signal levels: idle (mark, high voltage), and asserted (space, low voltage). (The polarity is a legacy from telegraphy, where the line was held high in order to show that the line was not broken, and that the transmitter was functional.)
If the line is held in the 'asserted' state for longer than a character time, this is called a break condition, and it can be detected by the receiver and signalled to the user specially. This is often used to interrupt the computer on the other end of the line.
