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By Root 1219 0

Multimedia I/O devices support video and sound functions. Specialty I/O devices run the gamut from common (touch screens) to rare (biometric devices). In fact, the exams deal with an entire set of I/O devices—networking devices—as completely distinct technologies. This book dedicates entire chapters to sound, printing, video, and networking, providing details about dealing with these types of devices and the ports they use. This chapter concentrates on two of the I/O device groups: the common devices and the specialty devices. You’ll learn how to identify and support both the most common and some of the most unusual I/O devices used in today’s PCs.

Essentials/Practical Application

Supporting Common I/O Ports

Whenever you’re dealing with an I/O device that isn’t playing nice, you need to remember that you’re never dealing with just a device—you’re dealing with a device and the port to which it is connected. Before you start looking at I/O devices, you need to take a look into the issues and technologies of some of the more common I/O ports and see what needs to be done to keep them running well.

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EXAM TIP This entire chapter shows up in both of the CompTIA A+ certification exams. Both exams test you on certain aspects of I/O devices, ports, configuration, and so on, so don’t skip this chapter.

Serial Ports

Finding a new PC with a real serial port is difficult, because devices that traditionally used serial ports have for the most part moved on to better interfaces, in particular, USB. Physical serial ports may be hard to find on new PC cases, but many devices—in particular, the modems many people still use to access the Internet—continue to use built-in serial ports.

In Chapter 8, “Expansion Bus,” you learned that COM ports are nothing more than preset I/O addresses and interrupt request lines (IRQs) for serial ports. Want to see a built-in serial port? Open Device Manager on a system and see if you have an icon for Ports (COM and LPT). If you do, click the plus (+) sign to the left of the icon to open it and see the ports on your system—don’t be surprised if you have COM ports on your PC. Even if you don’t see any physical serial ports on your PC, the serial ports are there; they’re simply built into some other device, probably a modem.

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NOTE Having trouble finding a PC with serial ports? Try a laptop—almost all laptops come with built-in modems.

Your PC’s expansion bus uses parallel communication: multiple data wires, each one sending one bit of data at a time between your devices. Many I/O devices use serial communication: one wire to send data and another wire to receive data. The job of a serial port is to convert data moving between parallel and serial devices. A traditional serial port consists of two pieces: the physical, 9-pin DB connector (Figure 18-1) and a chip that actually does the conversion between the serial data and parallel data, called the universal asynchronous receiver/transmitter (UART) chip. If you want to be completely accurate, the UART is the serial port. The port on the back of your PC is nothing more than a standardized connector that enables different serial devices to use the serial port. The UART holds all of the smarts that make the true serial port.

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NOTE Every UART in a system is assigned a COM port value. An internal modem snaps right into your expansion bus, so every internal modem has a built-in UART. Therefore, even though a modem doesn’t have a physical serial connection, it most certainly has a serial port—a built-in one.

RS-232 is a very old standard that defines everything about serial ports: how fast they communicate, the language they use, even how the connectors should look. The RS-232 standard specifies that two serial devices must talk to each other in 8-bit chunks of data, but it also allows flexibility in other areas, such as speed and error-checking. Serial came out back in the days when devices were configured manually, and the RS-232 standard has never been updated for automatic configuration. Serial ports are