I/O Ports and Devices . It also provides post- chapter review questions and answers. This chapter is from the book . There are a plethora of ports that connect these devices to the computer, for example, the well- known USB port. To fully understand how to install, configure, and troubleshoot input, output, and multimedia devices, you need to know the ports like the back of your hand. In this chapter you learn about serial, parallel, SCSI, USB, sound, and Fire. Wire ports and their corresponding devices; the goal is to make you proficient with the various interfaces you see in the IT field. The word . In this section, we detail input/output (I/O) ports. I/O ports allow for connections to hardware. This hardware could be internal or external. The ports are associated with copper circuits and memory ranges that allow the communication of data between the CPU, RAM, and the ports themselves. Common I/O ports include USB and Fire. Wire. In this section, we also discuss SCSI, audio connections, MIDI, and RG- 6 coaxial ports. Although the most important I/O port on recent systems is the USB port, you might also encounter other ports, including legacy ports such as serial and parallel, which we speak to in this section as well. USBUniversal Serial Bus (USB) ports have largely replaced PS/2 (mini- DIN) mouse and keyboard, serial (COM), and parallel (LPT) ports on recent systems. Most recent desktop systems have at least four USB ports, and many systems support as many as eight or more front- and rear- mounted USB ports. Figure 3- 1 shows the rear panel of a typical ATX system, including USB and other port types discussed in this chapter. Figure 3- 1 A typical ATX motherboard's I/O ports, complete with legacy (serial, parallel, PS/2 mouse, and keyboard), four USB, one IEEE 1. Ethernet, and audio ports. Serial ports are useful for transferring information between systems when other more traditional methods are unavailable. Programming the Serial Communications Port. The 68HC11F1 has two types of serial ports namely asynchronous (SCI) and synchronous (SPI). The most common form of communication device used in control is the SCI as this provides the user with a variable baud rate, stop bits, start bits, but no parity. Many PCs and compatible computers are equipped with two serial ports and one parallel port. There are two basic types of serial communications, synchronous and asynchronous. With Synchronous communications, the two devices initially synchronize. Most serial ports on personal computers conform to the RS-232C or RS-422 standards. A serial port is a general-purpose interface that can be used for almost any type of device. 2 Types Of Serial Ports For ComputersThe following sections describe USB port types and how to add more USB ports. USB Port Types, Speeds, and Technical Details. There are three standards types of USB ports you need to know: USB 1. USB 2. 0 (also called Hi- Speed USB)USB 3. Super. Speed USB)The standards use the same cable and connector types, which are shown in Figure 3- 2. USB cables use two types of connectors: Series A (also called Type A) and Series B (also called Type B). Series A connectors are used on USB root hubs (the USB ports in the computer) and USB external hubs to support USB devices. Series B connectors are used for devices that employ a removable USB cable, such as a USB printer or a generic (external) hub. Generally, you need a Series A–to–Series B cable to attach most devices to a USB root or external hub. Cables that are Series A–to–Series A or Series B–to–Series B are used to extend standard cables, and can cause problems if the combined length of the cables exceeds recommended distances. Adapters are available to convert Series B cables into Mini- B cables, which support the Mini- B port design used on many recent USB devices. USB 1. 1 ports run at a top speed (full- speed USB) of 1. Mbps), low- speed USB devices such as a mouse or a keyboard run at 1. Mbps, and USB 2. 0 (Hi- Speed USB) ports run at a top speed of 4. Mbps. USB 2. 0 ports are backward- compatible with USB 1. USB 1. 1 devices better than a USB 1. USB 3. 0 ports run at a top speed of 4,8. Mbps. USB packaging and device markings frequently use the official logos shown in Figure 3- 3 to distinguish the different versions of USB in common use. Note that the industry is shifting from using the term . Devices bearing these logos have been certified by the USB Implementers Forum, Inc. With either version of USB, a single USB port on an add- on card or motherboard is designed to handle up to 1. Starting with Windows 9. USB devices are Plug and Play (Pn. P) devices that are hot swappable (can be connected and disconnected without turning off the system). The USB ports (each group of two ports is connected to a root hub) in the computer use a single IRQ and a single I/O port address, regardless of the number of physical USB ports or devices attached to those ports. The maximum length for a cable attached to 1. Mbps or 4. 80. Mbps USB devices is five meters, whereas the maximum length for low- speed (1. Mbps) devices such as mice and keyboards is three meters. When a USB root hub is enabled in a computer running Windows, two devices are visible in the Windows Device Manager: a USB root hub and a PCI- to- USB universal host controller (USB 1. USB 2. 0), which uses the single IRQ and I/O port address required by USB hardware. If an external USB hub is attached to the computer, a generic hub also is listed in the Windows Device Manager (see Figure 3- 4). A root hub supports two USB ports. In Figure 3- 4, there are two root hubs listed, indicating that the system has four USB ports. You can access the Device Manager by clicking Start, right- clicking Computer (or My Computer in older Windows operating systems), and selecting Manage. The Computer Management window opens, and the Device Manager is located there. You can also access Device Manager from the Control Panel. Figure 3- 4 The USB section of the Windows XP Device Manager on a typical system. Note the fork- shaped USB logo next to the category and each device. Adding USB Ports. Need more USB ports? You can add USB ports with any of the following methods: Motherboard connectors for USB header cables. Hubs. Add- on cards. Some motherboards have USB header cable connectors, which enable you to make additional USB ports available on the rear or front of the computer. Some motherboard vendors include these header cables with the motherboard, whereas others require you to purchase them separately. Some recent case designs also include front- mounted USB ports, which can also be connected to the motherboard. Because of vendor- specific differences in how motherboards implement header cables, the header cable might use separate connectors for each signal instead of the more common single connector for all signals. USB generic hubs enable you to connect multiple devices to the same USB port and to increase the distance between the device and the USB port. There are two types of generic hubs: Bus- powered hubs might be built into other devices, such as monitors and keyboards, or can be standalone devices. A bus- powered hub distributes both USB signals and power via the USB bus to other devices. Different USB devices use different amounts of power, and some devices require more power than others do. A bus- powered hub provides no more than 1. A) of power to each device connected to it. Thus, some devices fail when connected to a bus- powered hub. A self- powered hub, on the other hand, has its own power source; it plugs into an AC wall outlet. It can provide up to 5. A of power to each device connected to it. A self- powered hub supports a wider range of USB devices, so it is recommended that you use it instead of a bus- powered hub whenever possible. You can also add USB ports by way of an expansion card. If you have a free slot in the computer, and know what type of slot it is, you can easily snap in an adapter card that has an additional two, four, or eight USB ports. The key is to make sure that the adapter card is completely compatible with the expansion slot on the motherboard. For example, if you have a PCI Express x. PCI Express x. 2 adapter card. We talk more about expansion cards and slots in Chapter 4, . The difference is possible because serial communications need only a few wires. Unlike parallel printers, which use a standard cable, each type of serial device uses a specially wired cable. DB- 9. M connectors are used on all but the oldest systems. Figure 3- 6 A typical DB- 2. F to DB- 9. M serial port converter. The DB- 2. 5F connector (lower left) connects to the 2. DB- 9. M port at the other end (upper right). A serial connection needs to have a cable that connects the device to the port. The device then uses the IRQ and I/O port settings assigned to the serial port. Let's discuss the cables and settings now. Types of Serial Cables. Serial cables can be constructed in many different ways. In fact, cables for serial devices are usually specified by device type rather than port type. This is because different devices use different pinouts. Some of the most common examples of serial cables include. Null- modem (data transfer) cable. Modem cable. A null- modem cable enables two computers to communicate directly with each other by crossing the receive and transmit wires (meaning that two computers can send and receive data, much like a computer network, though much slower). The best known of these programs is Lap. Link, but the Windows Direct Cable Connection/Direct Serial Connection utilities can also use this type of cable. Although these programs support serial cable transfers, parallel port transfers are much faster and USB transfers are much faster than parallel; these methods for direct connection are recommended for most versions of Windows. However, Windows NT 4. Figure 3- 7. Figure 3- 7 A Lap. Link serial cable with connectors for either 2. Only three wires are needed, enabling the cable to be much thinner than the 9- pin serial extension cable also shown. A modem cable is used to connect an external modem to a serial port. Some modems include a built- in cable, but others require you to use a DB- 9. F to DB- 2. 5M cable from the 9- pin connector on the serial port to the 2. What about serial printers? These printers are used primarily with older terminals rather than with PCs, and because different printers use different pinouts, their cables must be custom- made. In fact, I've built a few myself. Fortunately, most recent terminals use parallel or USB printers. Standard IRQ and I/O Port Addresses. Serial ports require two hardware resources: IRQ and I/O port address. Table 3- 1 lists the standard IRQ and I/O port addresses used for COM ports 1–4. Some systems and add- on cards enable alternative IRQs to be used, either through jumper blocks (older cards) or via software/Device Manager configuration (newer cards).
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