pp 210-221
Lesson 4.7 Ports regional
- Introduction
- The serial port
- The parallel port
- The keyboard and mouse ports PS / 2 type
- The corridor USB
When you have completed this course you will:
You name the regional ports has a personal computer
To mention the potential and limitations of each regional port
To describe the slots and connectors used for any type of regional port
Provide examples of devices connected to any type of regional port
4.7.1. Introduction
As we have seen the personal computer consists of four parts: the main unit, keyboard, mouse and monitor. The main components of the personal computer in the central unit, while the keyboard, mouse and monitor are peripheral devices.
Peripheral devices called all devices that are part of the personal computer and located outside the main drive. The peripheral devices connected to the central unit with the help of special cables.
The central unit can still connect other peripheral devices that expand the capabilities of the PC, such as printers, scanners, speakers and modems (modem). All peripheral devices connected to the central unit to specific ports, which ports are called peripherals. The holders of these doors are usually found on the motherboard behind specific openings in the box is the central unit to be connected to these peripherals. In some cases, the sockets of these doors are on expansion cards, which are linked to the expansion slots on the motherboard. The slots of these doors have access through special openings of the box is the central unit for expansion cards.
Then we will present the main regional ports.
4.7.2. The serial port
The most popular regional port of the PC is the serial port. This port follows the standard RS-232C, which is the most widespread standard serial communications. Because the implementation of serial communication is simple, is very common to have an RS-232C port on most devices that have the need to send or receive data. Such devices may be electronic cash registers, electronic scales, mobile phones, alarm systems, automotive electronics, industrial control systems applications, and printers, modem or mouse. All these devices can be connected to the serial port on the PC using the appropriate cable to enable data exchange. So for example you can connect your personal computer with an electronic cash register, to register with the help of appropriate software names and prices of products has a department store. Also, via the serial port can connect two computers together to exchange data.
A personal computer typically has two serial ports. The ports are named COM1 and COM2. Using appropriate expansion cards can be added to the PC serial ports also, called COM3, COM4, etc.
Figure 4.7.1: serial port connector 25 contacts (left) and 9 contacts (right)
Personal computers used two types of connectors for the serial port: the first is masculine type D 9 and the second contacts are male contacts type D 25. The two have exactly the same functionality. The only thing that changes is the shape and of course the kind of plug that should have the power with which to make the connection device to the serial port. The ATX type motherboards have built two serial ports with male connectors type D 9 contacts.
The serial port signals that appear at each contact of the socket shown in Table 4.7.2. As we understand it is easy to construct adapters (adapter) to allow the connection type connector contacts at D 9 D 25 type connectors contacts and vice versa. The adapters are enough to have a socket a plug type and one of the other type, the contacts of which are in accordance with Table 4.7.1, ie for example, the contact of host type 1 D 9 contacts with the contact of the connector 8 type D 25 contacts, the contact 2 to contact 3 etc.
Figure 4.7.2: The numbering of the contacts of the male host type D 9 contacts (top) and 25 contacts (bottom) as seen from the side that gets the plug.
Brand name
Contact reception type D 9 contacts
Contact reception type D 25 contacts
CD
1
8
RD
2
3
TD
3
2
DTR
4
20
GND
5
7
DSR
6
6
RTS
7
4
CTS
8
5
RI
9
22
Table 4.7.1: The serial port signals that appear at each contact of the socket
Figure 4.7.3: serial port adapter slot of type D 25 contacts in connector type D 9 contacts
The main disadvantage of the serial port is its low speed. The standard serial port RS - 232C transfers data at a maximum speed of 115Kbps (Kbps - Kilobits per second - thousands of bits per second). The latest serial ports can operate at speeds 230Kbps or even 460Kbps speeds but they are for today low. So the serial port used for communication with devices in which does not matter whether the data transfer rate or the volume of data transferred is very small.
4.7.3. The parallel port
The parallel port is one of the major ports of the PC. This port appears on all personal computers, by first appeared in 1981 until the most modern. In contrast to the serial port which is able to send 1 bit time (gradually, one after the other), the parallel port has 8 data lines, so you can send in parallel (simultaneously at the same time) 8 bits . This moreover is the reason why is called a parallel port.
The parallel port is designed to communicate the personal computer with a printer. So the 8 data lines as outputs operate only to the personal computer can send data to the printer, making the unidirectional parallel port. Addition of data lines parallel port has some extra lines for control signals to the printer. From these few lines are inputs, while others are outputs. For example, a control signal Paper end (End paper), which acts as an entrance and through the printer notifies the PC that the paper is finished. Instead, the signal is Initialize printer (Initialize - prepared the printer), which functions as an exit and sent from the PC to the printer to prepare for the final printing.
Figure 4.7.4: The parallel port connector
Personal computers to use the parallel port female connector type D 25 contacts. The parallel port signals that appear at each contact of the socket shown in Table 4.7.2.
Contact
Signal Description
Input / Output
1
Strobe
Exit
2
Data bit 0
Exit
3
Data bit 1
Exit
4
Data bit 2
Exit
5
Data bit 3
Exit
6
Data bit 4
Exit
7
Data bit 5
Exit
8
Data bit 6
Exit
9
Data bit 7
Exit
10
Acknowledge
Entrance
11
Busy
Entrance
12
Paper end
Entrance
13
Select
Entrance
14
Auto feed
Exit
15
Error
Entrance
16
Initialize printer
Exit
17
Select input
Exit
18 to 25
GND
-
Table 4.7.2: The parallel port signals that appear at each contact of the host
Figure 4.7.5: The numbering of the host female contacts type D 25 contacts
As shown in Table 4.7.2, there are five input signals, which are used to inform the printer to a PC for the state. With some tricks these signals can be used to transfer data to and from the opposite direction. It is possible for example to connect two PCs together to share data. In this case, of course, can be transported simultaneously in each direction at most 5 bits of data.
The speed of the parallel port can be up to 140 KBytes / sec, which makes it significantly faster than the serial port, which can reach a maximum of 460Kbps (about 46 KBytes / sec).
The parallel port, as described above, was the first personal computers. With the development of technology came new, improved versions of this port. So, first appeared in the duplex (bi-directional) parallel port, which allows through 8 data lines to transfer data in both directions of data transfer speed can be up and 300 KBytes / sec. Then came the parallel ports EPP (Enhanced Parallel Port - Enhanced Parallel Port) and ECP (Enhanced Capabilities Port - Port increased capacity). The ports are broadly consistent with the simple or bidirectional parallel port, but also allow devices specifically designed for them to transfer large data rates of up and 2MBytes/sec.
A personal computer is usually a parallel port, which is called LPT1. Indeed, the type ATX motherboards are built to accommodate the parallel port. Using appropriate expansion cards you can add extra PC parallel ports, called LPT2, LPT3, etc.
Despite the fact that the parallel port was designed specifically to connect a printer to modern personal computers used to connect a multitude of external devices. This happens kitten parallel port found in most personal computers and has an increased data transfer speed compared to the serial port. Therefore, it is ideal for connection to external PC devices without having to place an adaptive expansion card. Thus, in addition to parallel port printers can connect scanners, modem, storage devices such as CD-ROM drives and tape drives or cameras.
4.7.4. Doors keyboard and mouse PS / 2
The keyboard is absolutely necessary for the operation of personal computer. So next is to have its own door, the reception which is always located on the motherboard. Especially motherboards baby AT type keyboard connector is the only regional port connector that is glued onto the motherboard. The connector type is female DIN five contacts.
In type ATX motherboards have a slightly different connector for the keyboard. The connector type is female mini-DIN six contacts are a little smaller than the corresponding socket motherboards baby AT type, called type connector PS / 2.
Figure 4.7.6: The connector DIN (left) and mini-DIN (right) port of the keyboard
The keyboard type PS / 2 took its name from the computer's PS / 2 IBM, which was originally used in such a connector for the keyboard.
Due to the different keyboard with motherboards, there are two types of keyboards:
AT type keyboards that are on the edge of the cable type a male DIN connector contacts and five related to the corresponding socket motherboards baby AT type
-type PS / 2 with the edge of the cable to a male type connector mini-DIN six contacts and connected to the corresponding socket of type ATX motherboards
The keyboards of these two types is basically the same. The only difference is the plug at the end of the cable. For this reason there are adapters that allow connection of AT type keyboards to type ATX motherboards and keyboards type PS / 2 motherboards to release baby AT. These adapters are nothing more than a slot on the plug the keyboard, and a connector that plugs into the motherboard. The socket and plug the adapter properly connected by a special cable.
Similarly there are two types of mice:
the serial mice, which are connected to one of the serial ports of your computer and used mainly in computers motherboard type baby AT, which has a special port for the mouse
the mouse PS / 2, connected to the motherboards type ATX, which have a female jack type mini-DIN six contacts with the same type keyboard PS / 2. These two slots but do not correspond to identical ports, which means that we can not connect the keyboard connector on the mouse and vice versa. Next to these jacks is always a symbol, so that we can see the keyboard connector from the slot of the mouse.
The mice of these two types is not necessarily the same. Some mice are designed to operate in PS / 2 port and some a serial port. But there are mice that can run on both ports. These mice usually have plug port PS / 2 and may be connected to serial port with a suitable adapter.
4.7.5. The corridor USB
The corridor USB (Universal Serial Bus - Universal Serial corridor) corridor is a serial data transfer at very high speed. In this corridor can connect two devices to 127. The communication between these devices occurs at 1.5 or 12 Mbps.
In one hallway is always connected to USB host a USB (USB host) which controls the operation of the corridor. USB devices connected to the corridor can be exchanging data with the host. In a personal computer USB host built into the motherboard or an expansion card is placed in one of the expansion slots. The host has a USB port on the USB that can connect a device to USB. To connect more devices requires the use of a hub USB (USB hub). The hub connects USB port on the host and has numerous ports on which they can connect various devices to USB. A node can also be connected to another node, thus increasing the available USB ports as shown in Figure 4.7.7.
Figure 4.7.7: Topology corridor USB
The corridor USB was designed to be simple to use. So, all you have to do to connect a USB device in the personal computer is to put the cable into the appropriate slot on the computer. The USB port connection combines the simplicity of serial and parallel port with high speed data transfer which makes it ideal for connecting external devices to the PC. Next, then, over time the USB port to replace serial and parallel port.
Figure 4.7.8: The USB port connector and the corresponding connector
The USB corridor is established in modern personal computers. The modern type ATX motherboards often have an embedded host and a USB hub offers two USB ports for connecting devices. Such devices can be scanners, printers, keyboards, mice, speakers, telephones, monitors, appliances, modem, cameras or storage devices.
4.7.6. Summary
As we saw, each regional port has its own special characteristics that make it more or less suitable for connection of various devices. Table 4.7.3 seem clustered features of the main regional ports used in personal computers and some of the most representative devices that can connect to them.
Type of port
How to transfer data
Data Transfer Rate
Devices connected
RS-232C
serially
up to 115Kbps, 230Kbps or 460Kbps
cash registers, electronic scales, mobile phones, alarm systems, car electronics, printers, modem, mouse
parallel
parallel
140 KB / sec
300 KB / sec (bidirectional)
2MB/sec
(ECP and EPP)
printers, scanners, modem, drivers CD-ROM, tape drives, cameras
USB
serially
1.5 or 12 Mbps
scanners, printers, keyboards, mice, speakers, telephones, monitors, appliances, modem, cameras, storage devices
Table 4.7.3: Characteristics of regional ports
What did you learn
The regional ports used to connect peripheral devices to the motherboard.
The serial port is a widespread low-speed port which is used to connect a variety of devices.
The parallel port, although it was designed to connect the printer, because of the relatively high-speed data transfer supports, is also used to connect a large number of peripherals.
The corridor is a USB high-speed corridor is very simple to use and designed to replace serial and parallel port.
Terminology
serial port, RS-232C, plug and socket type D 9 and 25 contacts
parallel port, simplex, duplex, ECP, EPP
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