3.3.7. I / O Ports and Peripherals

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I / O ports are ports and INPUT / OUTPUT devices that enable computers to connect with various external devices through the purpose-built port-connector interfaces or devices within the casing system are complimented on the motherboard or on a card that is inserted the slot. Most newer motherboards have extra connectors that allow them to connect to external connectors mounted on sheet metal brackets on the back of the computer or with special performances of facades physical size FDD or CD player, which is installed in front of the computer case, which include connectors for connecting USB devices , microphones, headphones, slots for inserting memory cards and similar devices, or for an entirely different purpose, such as the regulation of rotation of the CPU fan heatsink. Each device communicates with the computer via electronic logic circuits that connect the device to one of the bus system, and about the way of communication taking care program routines incorporated as an integral part of the BIOS and the available options chipsets and motherboards that uses the records in the BIOS , and in the end, the possibilities of your operating system.

So, the logic circuits of I / O ports are essentially electronic gate that would allow controlled by a microprocessor-way or two-way flow of data between the device and the microprocessor, memory, disk, or other assembly computer via a bus system. Logic circuits I / O ports are part of the motherboard circuits for devices that are on the card for general purpose terminals as a keyboard, and floppy disk device, a standard parallel or serial port, and so on.

Electronic logic circuits I / O ports of additional devices can be realized within the framework of the additional devices such as I / O port NICs incorporated on the card itself as strictly dedicated integrated circuit (chip) that part of the task the CPU takes on . Way communication with every type of device is not the same. You may be required to the computer to communicate with multiple devices of the same type. But with only one computer can work simultaneously and exchange commands and data bus. Because each of the pots must have its own separate ADDRESS at which recognizes a group of more of them will have the same task, and serve them the same as programming routines for the two ports provided for serial communication will each have access to 4 different possible addresses from which he only one can be assigned and will serve the same BIOS software routines.

There are three basic ways to transfer data through the I / O ports:

1.) PARALLEL - PIO 
    (Programmed Input/Output)

2.) SERIAL -- UART 
    (Universal Asynchronous Receiver Transmitter)

3.) SERIAL -- USB
    (Universal Serial Bus)

PARALLEL data indicates the simultaneous transmission of bits over multiple communications lines. Arrangements have been standardized and are directly linked to all three buses. The complex has its own register (cache), which has its own address so the microprocessor can easily transfer to the data. External devices that are connected to a circuit for parallel transmission may be different (printer, ZIP drive, etc.), and for each of them performs programming PIO specially made program according to the type of device that is loaded into the working memory and executed before the data transfer. In this way it becomes specifically PIO interface between the computer and the connected device.

 Parallel communication
Figure 3.3.22 Principal of eight bit parallel transfer.

The principle of parallel transmission is shown in Figure 3.3.22, where he observed a significant two-way flow of information. The PIO are transmitting and receiving electronic circuitry which include alternate (HALF-DUPLEX) or for simultaneous transmission in both directions using two PIO (FULL-DUPLEX).

The concept of water transfer involves two conductors, which means that for such a transfer to 16 data lines. But one of lines is ground, then total number of lines for the transmission drops to 9 because the ground wire common to all lines. In various combinations of control over the total number of necessary transfer guide can be most 24th Very often integrated into one casing assembly includes two PIO devices of the same properties.

The presented system parallel data transmission developed by CENTRONICS, and is often so called. As bits simultaneously undergoing transfer is faster than serial transmission, but unsuitable for remote connections because of the large number of guides in the connecting cable. Efficient to cable length of 10 m.

The printer is very common devices that are connected on the PIO as A/D and D/A converters signal, respectively converting analogue signals to digital and vice versa. A/D converters are usually components of measurement systems that follow a process, and that the computer used for the storage and processing of the measured process variables. D/A converters usually provide an output signal as a result of the analysis in the computer that controls the valve or some engine and in this sense it is the automatic control of the process. In everyday practice, the widespread use of D/A converters in the music CD and just the quality of this conversion determines the class, the quality and price of these music devices.


Example IX

The principle of an analog / digital converter.

A/D converter is not converted to digital form entire analog signal, samples but only in time (Figure 3.3.23).

 Sampling
Figure 3.3.23 Sampling analog signals in time.

Sampling density will determine the quality of 'tracking' as an analog signal. Between the two sampling effects the change of sample size in binary combination. This means that for the 8-bit binary combinations of sample size can join one of 256 binary combinations. Increased number of bits in combination will enable finer 'monitoring' sample size - resolution. Higher sampling density and makes more complex the higher the resolution making the A/D converter.

SERIAL data have long been used in computer technology and is commonly used for RS 232C serial interface (interface). Electronic circuits and serial interfaces are receiving and transmitting part, but communication is alternating (HALF-DUPLEX). To communicate the need of at least one cable (two conductors). Data are transmitted pulse per pulse and therefore communication is very slow.

To make the data bus to be able to send a sequence via the serial interface in the interface must have a built-in offset registers that allow parallel conversion accepts the serial transmit and vice versa (Figure 3.3.24).

 Serial communication
Figure 3.3.24 Principle of serial data transfer.

Between the two serial ports on two computers serial communications wiring would be achieved by the following Figure.

 Null-modem wiring
Figure 3.3.25 Serial communication.

To modify the data used TX and RX connectors, basically a necessary condition to achieve communication. DTR and DSR signals are used when communication is established and they are constantly active during the communication. If one of them fails communication is interrupted. DTR signal is sent to a device that wants to communicate, and DSR was called to answer the communication is possible and of receiving communications established. RTS is an output signal that is sent to the other device is ready to accept data, and then expect a confirmation in the form of the CTS input signal as notification of the other device to transmit data can begin. These two signals handshake data exchange established by communication. DCD is a signal that is commonly used in modem communications. Transmitted from the device to which the connection is established, and it is then returned. Its continuity points to maintain communication. For the DCD signal can be used DTR or RTS signal. The modem communications used since RI port on which the signal from the signal when it is ringing phone (B.B.S. communication).

All the above signals can be transferred to a special device remotely over the existing postal network, designed specifically for this purpose, called MODEM (MOdulation-DEModulation). How PTT classic lines and exchanges that do not have additional equipment not designed for the transmission of digital signals, the modem is in the process of sending them into a AC signal on the principle of variable frequency and the reception back to digital (Figure 3.3.26).

 Modem Communication
Figure 3.3.26 Conversion process signals to the modem communication.

Cited in practice means that wherever possible voice communication, regardless of the distance from the central telephone set, it is possible to modem communication, as in the case of better ties occur with greater speed and fewer errors. During the initial connection to the modem with an access device in the PTT headquarters 'arrange' optimal speed communication. Of course, the signal frequencies that are used in modem language area, that classical operator can transmit.

As computers have the same pinout connector for serial interface can not be connected directly to the first pin (contact in connector) to the first pin one another, since the transmitter of one device was connected to the transmitter of the other device. Therefore, the connection between the computer has to be done where the cable lines 'crossed' as shown in Figure 3.3.25. But if the serial port of the computer connects to the modem or printer, this intersection is not necessary because the connection of these devices is envisaged to replace cables.

Therefore be distinguished:

            MODEM CABLE = lines for connection to the modem are not crossed.
            NULL-MODEM CABLE = crossed lines of communication between computers.

Sam communication is the transfer of blocks of data, typically a few kB in size which are added to mark the beginning and end of the block and the checksum error (CRC).

How modern modems are used in the process of teaching them specific protocols like Xmodem, Zmodem, etc. and also perform data compression before sending the PTT line increases the speed of data transfer, but not the speed of communication. But the speed of communication between the serial port and the modem can be several times higher. Communication speed between the modem has not exceeded the limit of 100'000 Bd, and this method of data transmission is one of the slowest. Far more effective communication is achieved by connecting computers on the network type Ethernet, Token Ring and the like, and to connect local home infrastructure network system as ADSL solution is versatile and efficient.

If the serial port, plug in the mouse, a special program to support through one of the output signal lines power electronics mouse while holding the signal line permanently open. Via the input lines to receive information about the vertical and horizontal scrolling mouse capable switches, which its program support (mouse driver) is converted into the corresponding data for the execution of tasks and display. Communication between the mouse and the computer in this case is one-way (SIMPLEX).

USB (Universal Serial Bus) is an advanced technological solution for connecting external devices to your computer. USB technology is the goal of streamlining the bus master computer of the special expansion cards, as well as to facilitate insertion and disconnecting external devices, and their automatic recognition (plug-and-play) without the need to restart (reboot). Serial data is exchanged, and during the development of the next version accepted:

Standard Baud Rate
USB 1.0 1.50 Mbps
USB 1.1 12.00 Mbps
USB 2.0 480.00 Mbps
USB 3.0 4'800.00 Mbps
USB 3.1 10'000.00 Mbps

USB is asymmetric design, and consists of a multi-server and multiple units that include the server as a branch through special devices (hub) and thus generate the trees are rooted form. When USB is possible to have 5 levels of branching for each controller server, you can connect 127 devices less the number of hub-ins that are attached to the same USB server. Currently there are two standard USB connectors:

Each of these standards define two types of connectors: the ' A ' standard for the computer and the ' B ' standard for the device. Very important is the 'range' of communication between devices that is 5 m, i.e. it is the maximum permissible length of cable. If you use a longer cable than the above, can be realized and the USB connection device will correctly display computer, but it will not be the correct communications. Using long communication cable from the specified value has no meaning. If you are using a USB-HUB between the USB device and the computer can be specified to increase the distance. A better solution to the USB adapters-UTP (USB Extender), which permits communication to 45 m between computers and devices. These adapters are powered via the USB connectors computers. The power source is a 5 V USB connectors, and power consumption depending on the type of device.

USB 3.0 standard provides for the use of optical fiber (full-duplex), which implies greater communication distances between devices. USB 3.1 standard has two significant innovations: the connector is physically different and symmetrical and is all the same to be connected and provides for the use of adapters for connecting older devices, the communication speed is increased due to use of different coding schemes signal (128b/132b instead 8b/10b) that is compatible with the older scheme and electrically accepts older devices.

In addition to USB standards based and IEEE 1394 protocol that support 'FireWire' devices (Apple) or 'i.Link' devices (Sony). One of the oncoming bus protocols. The difference between 'i.Link' and 'FireWire' is what 'i.Link' no wires to power the device via the bus. The goal of the protocol is to provide a very fast and cheap communication that is easy to use. The protocol is also highly scalable, allows 'asynchronous' and 'synchronous' application, permission to access a vast amount of memory mapped address space, and perhaps most importantly Peer-to-Peer (P2P) connection. Supported baud rates are 100 Mbps, 200 Mbps and 400 Mbps, and it is the specification that will allow speeds of 800 Mbps, 1600 Mbps and 3200 Mbps. 'Range' of communication between devices is 10 m, but as in the previous case can increase adapters. Source of supply of 30 V. USB and IEEE 1394 are duplex communication.

In asymmetrical, of very great importance fast synchronous serial communication used by PCI Express devices, without which the quick work of modern computer systems is unthinkable. The transfer of the larger group of pulses with shorter duration and quality of synchronization are realized higher data transfer rates.

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