- Db25 Parallel Interface
- Parallel And Serial Connections
- Distinguish Between Serial And Parallel Interface
Think about a modem. Although the RS-323 interface driven by a UART chip may be banging out the bits one at a time, the actual encoding done by the modem may use parallel encodings whereby multiple bits are transmitted at the same time. Ethernet also used to be strictly serial (baseband pulses at a rate of 10 Mhz). Parallel Ports. Of the two, the parallel port is the older port design with the first use in the early 1970s, allowing printers to be hooked directly into a mainframe and print orders carried out by entering a section of code through the command station. The parallel port allows for a one-way transmission of data from the source to a secondary device, such as a printer.
I would like to know whether the DB-25 port is a serial or parallel port. These ports are otherwise known as printer ports, aka LPT port.
I'm very confused about this since, according to Wikipedia, this port is considered part of the D-Subminiature connectors, which are mostly used for RS-232 serial communication.
On the other hand, we know that this port is known as the parallel printer port. So, why all this confusion? Is this confusion only associated with DB-25 ports on computers? Then how about other devices that have DB-25 connectors (mostly male DB-25)?
2 Answers
Is DB-25 port Serial or Parallel?
A DB-25 connector could be serial port or parallel port or something else.
A DB-25 connector is a generic connector.
It is not exclusively used by just one interface (like HDMI or USB connectors are).
On a modern PC, a DB-25 (especially a female connector) is typically associated with a parallel (aka LPT) port.
On older computer and telecommunication equipment, a DB-25 connector is typically a RS-232 serial port.
Amd radeon settings download. Prior to the mid-1980s, RS-232 ports typically used DB-25 connectors.
Printers used RS-232 interfaces and/or custom interfaces.
One of those interfaces, a parallel interface using a 36-pin connector developed by Centronics, became an industrial and then an IEEE standard.
When IBM introduced its PC, it substituted the large Centronics connector with a slimmer female DB-25 for the LPT port. The female DB-25 connector was typically used for DCE RS-232 ports (e.g. a phone modem), and this was a new application for that connector. The RS-232 port(s) on the IBM PC used male DB-25 connector(s).
When IBM introduced its second-generation PC/AT, in 1984, IIRC it substituted the large male DB-25 connectors for RS-232 ports with 'DB-9' (actually a DE9) connectors that today's users associate with 'serial' ports. The parallel LPT port continued to use the female DB-25 connector.
sawdustsawdust
Db25 Parallel Interface
The connectors themself arn't actually specific to a protocol - It simply refers to the number of pins and that its sub miniature. You could in theory wire up any suitable connector to the right electrical connections and to use it.
In most systems I've seen, serial ports had 9 pins (since they didn't implement the whole 25 pin standard). I could also have, in theory the same 9 pins on a mini DIN connector or used the same 9 or 25 pins for another protocol.
On the other hand, printers often had a centronics port rather than a DB25, and once again, the physical connector simply had to support the minimum amount of pins the electrical standard needed.
At the end of the day the smart thing is to check before you plug anything in ;p
Journeyman Geek♦Journeyman Geek
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In telecommunication and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are sent as a whole, on a link with several parallel channels.
Serial communication is used for all long-haul communication and most computer networks, where the cost of cable and synchronization difficulties make parallel communication impractical. Serial computer buses are becoming more common even at shorter distances, as improved signal integrity and transmission speeds in newer serial technologies have begun to outweigh the parallel bus's advantage of simplicity (no need for serializer and deserializer, or SerDes) and to outstrip its disadvantages (clock skew, interconnect density). The migration from PCI to PCI Express is an example.
Cables[edit]
Many serial communication systems were originally designed to transfer data over relatively large distances through some sort of data cable.
Practically all long-distance communication transmits data one bit at a time, rather than in parallel, because it reduces the cost of the cable. The cables that carry this data (other than 'the' serial cable) and the computer ports they plug into are usually referred to with a more specific name, to reduce confusion.
Parallel And Serial Connections
Keyboard and mouse cables and ports are almost invariably serial—such as PS/2 port, Apple Desktop Bus and USB.
The cables that carry digital video are almost invariably serial—such as coax cable plugged into a HD-SDI port, a webcam plugged into a USB port or Firewire port, Ethernet cable connecting an IP camera to a Power over Ethernet port, FPD-Link, etc.
Other such cables and ports, transmitting data one bit at a time, include Serial ATA, Serial SCSI, Ethernet cable plugged into Ethernet ports, the Display Data Channel using previously reserved pins of the VGA connector or the DVI port or the HDMI port.
Serial buses[edit]
Many communication systems were generally designed to connect two integrated circuits on the same printed circuit board, connected by signal traces on that board (rather than external cables).
Integrated circuits are more expensive when they have more pins. To reduce the number of pins in a package, many ICs use a serial bus to transfer data when speed is not important. Some examples of such low-cost serial buses include RS-232, SPI, I²C, DC-BUS, UNI/O, 1-Wire and PCI Express. In IC, serial bus may be typically implemented by using multiplexer (which utilizes technique called multiplexing).[1]
Serial versus parallel[edit]
The communication 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 simultaneously along multiple channels (e.g., wires, printed circuit tracks, or optical fibers); whereas, a serial link transmits only a single stream of data.
Although a serial link may seem inferior to a parallel one, since it can transmit less data per clock cycle, it is often the case that serial links can be clocked considerably faster than parallel links in order to achieve a higher data rate. Several factors allow serial to be clocked at a higher rate:
- Clock skew between different channels is not an issue (for unclocked asynchronous serial communication links).
- A serial connection requires fewer interconnecting cables (e.g., wires/fibers) 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 proximity.
Distinguish Between Serial And Parallel Interface
In many cases, serial is cheaper to implement than parallel. Many ICs have serial interfaces, as opposed to parallel ones, so that they have fewer pins and are therefore less expensive.
Examples of architectures[edit]
- ARINC 818 Avionics Digital Video Bus
- Atari SIO (Joe Decuir credits his work on Atari SIO as the basis of USB)
- CAN Control Area Network Vehicle Bus
- ccTalk Used in the money transaction and point-of-sale industry
- CoaXPress industrial camera protocol over Coax
- DC-BUS communication over DC power lines
- DMX512 control of theatrical lighting
- Fibre Channel (high-speed, for connecting computers to mass storage devices)
- InfiniBand (very high speed, broadly comparable in scope to PCI)
- I²C multidrop serial bus
- MIDI control of electronic musical instruments
- RS-232 (low-speed, implemented by serial ports)
- RS-422 multidrop serial bus
- RS-485 multidrop multimaster serial bus
- SDI-12 industrial sensor protocol
- SONET and SDH (high speed telecommunication over optical fibers)
- SpaceWire Spacecraft communication network
- T-1, E-1 and variants (high speed telecommunication over copper pairs)
- Universal Serial Bus (for connecting peripherals to computers)
- UNI/O multidrop serial bus
- 1-Wire multidrop serial bus
See also[edit]
- High-Level Data Link Control (HDLC)
- Universal asynchronous receiver/transmitter (UART)
References[edit]
- ^'Circuit Implementation Using Multiplexers'. www.ee.surrey.ac.uk. Retrieved 2019-04-30.
External links[edit]
- Serial Interface Tutorial for Robotics (contains many practical examples)