Ports and Interface

Ports and Interface: The various port on the computer allow it to communicate with the many different devices and peripherals attached. The connectors on the back of your computer may also be called as input / output ports ( i/o ports ) or communication ports.

The first thing to know is the different between a male and female connector. The male connector fits inside the female connector. If the connector has pins protruding from it, it’s a male connector. If the connector has holes for the pins to fit into, then it’s a female connector.

The second thing you should remember is that when you join a connector to a port, they must have the same shape and the same number of pins or holes.

The various I/O ports are Serial, Parallel, PS/2, USB & firewire port. Out of the I/O ports mentioned except the USB and firewire ports, the other ports are not hot swappable. USB and Firewire ports are the only ports that should be considered hot-swappable ( this means they can be plugged in or unplugged while the machine is on ).

External ports ( which are linked to the motherboard ) allow users to connect devices such as scanner, printers, mice and keyboards.

Serial: A serial port can be used to connect many types of devices. Data is transferred to and from the device one bit at a time.

Parallel: A parallel port usually has a 25-pin connector and is most often used to connect local printers. Devices attached to a parallel port are capable of receiving more than one bit of data at a time.

PS/2: PS/2 ports are used to connect the mouse and the keyboard.

Serial and parallel ports are currently considered to be “legacy ports” since they use old technology for data transfer. Never technology includes the following.

Serial and parallel ports are currently considered to be “legacy ports”. Since they use old technology for data transfer. Newer technology includes the following:

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USB  1.1 – USB Basic Speed: USB (Universal Serial Bus )is an external bus standard that supports data transfer rates of 12 Mbps (12 million bits per seconds). A single USB port can be used to connect up to 127 peripheral devices, such as mice, modems, and keyboard. USB also supports plug and play installation and “hot plugging”, meaning you do not have to shut down the computer in order to attach or detach a device from the machine.

USB 2.0 – USB Hi-Speed: USB 2.0 is a new version of the USB specification. This new port is backwards-compatible, allowing older USB 1.1 devices to connect and update without trouble. However, the new USB Hi-Speed ports support data transfer rates of 480 Mbps, even faster than FireWire ports.

USB 3.0 – USB SuperSpeed: USB 3.0 defines a new SuperSpeed transfer mode, with associated new backwards-compatible plugs, receptacles, and cables.

The new SuperSpeed mode provides a data signaling rate of 5 Gbit/s and the specification considers it reasonable to achieve only around 3.2 Gbit/s (0.4 GB/s or 400 MB/s)

FireWire: FireWire is a very fast external bus standard that supports data transfer rates of up to 400 Mbps. FireWire is also known as IEEE 1394. A single 1394 port can be used to connect up to 63 external devices and is much faster than USB 1.1. it supports both plug and play and hot plugging and also provides power to peripheral devices.

COM and LPT Assignments

Port	I/O Address	IRQ
COM 1	3F8	4
COM 2	2F8	3
LPT1	378	7
LPT2	278	5

Asynchronous and Synchronous communication

There are two schemes of transmitting data to be ports.

Asynchronous                     Synchronous

In the asynchronous scheme, each character is transmitted with the start bit and the stop bit as the synchronization bits.

In the synchronous scheme, a bit pattern called sync is transmitted after a fixed number of data bytes.

Asynchronous communication is generally used with slow peripherals, whereas very high speed transmission is possible with the synchronous communication scheme.

Serial Interface: PC support two serial interfaces Each is an RS-232 standard interface. The PC supports asynchronous and synchronous communication. Synchronous communication is rarely used, it is used only for high speed communication between PC’s. Asynchronous communication is widely used in PCs.

The RS232 Serial Interface: The RS-232 interface is a standard interface specified by the Electronic Industries Association ( EIA ) and is followed by the manufacturers of computers and data communication products ( RS stands for Recommended Standard ). RS-232 was basically designed to allow computing devices called equipment (DTE) to talk to communications devices called data circuit-terminatting equipment (DCE). So there is a DTE-type RS-232 interface and a DCE-type RS-232 interface. RS-232 is designed to allow DTEs to talk only to DCEs. Rs-232 used DB25 and DB9 connectors. Male connectors go on the DTEs; female connectors go on the DCEs.

Parallel ( Centronics ) Interfaces/IEEE 1284

The most common method of attaching a printer to a computer is through a simple interface called the Centronics interface. The original parallel ports had eight outputs, five input and four bidirectional lines. A  parallel ports transfer multiple bits at once, while a serial ports transfer a bit at a time. Pc can support up to three parallel ports. They are named LPT1 ,LPT2 and LPT3; the name refers to Line Printer 1 2 and 3.

PS/2 port: This port was designed by IBM for their Personal System /2 computers. The PS/2 port has lived on in other computers as the standard for keyboard and mice. Most computers come with two PS/2 ports.

USB ( Universal Serial Bus ): USB s peripheral bus standard developed by PC and telecom industry leaders – Compaq,  DEC, IBM etc that brings plug and play of computer slots and reconfigure the system. Personal computer  equipped with USB allows computer peripherals to be automatically configured as soon as they are physically attached – without the need to reboot or run setup. USB also allow multiple devices – up to 127 – to run simultaneously on a computer, with peripheral such as monitors and keyboards acting as additional plug – in sites, or hubs.

Digital Visual Interface: Digital Visual Interface ( DVI ) is  a video display interface developed by the Digital Display Working Group ( DDWG ). The digital interface is used to connect to a video source, such as a video display controller to a display device, such as a computer monitor.

Display Port: Display Port is a digital display interface developed by the Video Electronics Standards Association ( VESA ) the interface is primarily used to connect a video source to a display device such as a computer monitor, though it can also be used to carry audio, USB, and other forms of data.

Video Graphics Array: A Video Graphics Array ( VGA ) connector is a three-row 15-pin DE-15 connector. The 15-pin VGA connector was provided on many video cars, computer monitors, laptop computers, projectors, and high definition television sets. On laptop computers or other small devices, a mini-VGA port was sometimes used in place of the full-sized VGA connector.

SCSI ( Small Computer System Interface ) Basics: SCSI is a set of ANSI standard electronic interfaces that allow personal computers to communicate with peripheral hardware such as disk drives, tape drives, CD – ROM drives, printers and scanners faster and more flexibly than previous interface.

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