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| In ] and ], '''serial communications''' refers to any data transmission scheme in which data is sent one symbol at one time, sequentially over a communications channel. |
In ] and ], '''serial communications''' refers to any data transmission scheme in which data is sent one ] at one time, sequentially over a ]. | ||
| ==Serial versus parallel== | |||
| The communications links across which computers—or parts of computers—talk to one another may be either serial or parallel. A parallel link transmits several streams of data (perhaps representing particular bits of a stream of bytes) along multiple channels (wires, printed circuit tracks, optical fibres, etc.); a serial link transmits a single stream of data. | The communications links across which computers—or parts of computers—talk to one another may be either serial or parallel. A parallel link transmits several streams of data (perhaps representing particular bits of a stream of bytes) along multiple channels (wires, printed circuit tracks, optical fibres, etc.); a serial link transmits a single stream of data. | ||
| At first sight it would seem that a serial link must be inferior to a parallel one, because it can transmit less data on each clock tick. However, |
At first sight it would seem that a serial link must be inferior to a parallel one, because it can transmit less data on each clock tick. However, it is often the case that serial links can be clocked considerably faster than parallel links, and acheive a higher data rate. A number of factors allow serial to be clocked at a greater rate: | ||
| ⚫ | *] between different channels is not an issue (for unclocked serial links) | ||
| *A serial connection takes up less space. | |||
| *The extra space |
*A serial connection requires fewer interconnecting cables (e.g. wires/fibres) and hence occupies less space. The extra space allows for better isolation of the channel from its surroundings | ||
| *Crosstalk is less of an issue, because there are fewer conductors in close proximity. | |||
| *Not having multiple conductors in close proximity means less crosstalk at higher frequencies. | |||
| ⚫ | *Clock skew between |
||
| *These last three considerations mean that a serial connection can, all else being equal, be clocked considerably faster than a parallel one. | |||
| In many cases, serial is a better option because it is cheaper to implement. Many ICs have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore cheaper. | |||
| ⚫ | ==Examples of serial communication architectures== | ||
| ⚫ | ==Examples of serial communication architectures== | ||
| *] ] | *] ] | ||
| *] (old, low-cost, low-speed, |
*] (old, low-cost, low-speed, implemented by ]) | ||
| *] | *] | ||
| *] (newer, moderate-speed, for connecting computers to peripherals) | *] (newer, moderate-speed, for connecting computers to peripherals) | ||
Revision as of 16:20, 2 June 2005
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In telecommunications and computer science, serial communications refers to any data transmission scheme in which data is sent one symbol at one time, sequentially over a communications channel.
Serial versus parallel
The communications links across which computers—or parts of computers—talk to one another may be either serial or parallel. A parallel link transmits several streams of data (perhaps representing particular bits of a stream of bytes) along multiple channels (wires, printed circuit tracks, optical fibres, etc.); a serial link transmits a single stream of data.
At first sight it would seem that a serial link must be inferior to a parallel one, because it can transmit less data on each clock tick. However, it is often the case that serial links can be clocked considerably faster than parallel links, and acheive a higher data rate. A number of factors allow serial to be clocked at a greater rate:
- Clock skew between different channels is not an issue (for unclocked serial links)
- A serial connection requires fewer interconnecting cables (e.g. wires/fibres) and hence occupies less space. The extra space allows for better isolation of the channel from its surroundings
- Crosstalk is less of an issue, because there are fewer conductors in close proximity.
In many cases, serial is a better option because it is cheaper to implement. Many ICs have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore cheaper.
Examples of serial communication architectures
- Morse code telegraphy
- RS-232 (old, low-cost, low-speed, implemented by Serial Ports)
- RS485
- Universal Serial Bus (newer, moderate-speed, for connecting computers to peripherals)
- FireWire
- Fibre Channel (high-speed, for connecting computers to mass storage devices)
- InfiniBand (very high speed, broadly comparable in scope to PCI)
- Serial Attached SCSI
- Serial ATA
- PCI Express