CHAPTER 10 I/O PORTS AND DEVICES

	Introduction :
	Input/Output ports (I/O) enable you to connect hardware devices such as the keyboard, mouse, printer and scanners to the system. It is the entry and exit point for data from the system. I/O ports give you freedom in choosing and installing the device because if you have only few ports you can select a device that is available for that port.
10.1 Introducing Ports
	A port is used to connect the system and a device together, using a connecting cable, so that they can communicate together. The different ports available are usually located at the back of the system case. They may also be located at the front or the side of the system case.
	System Case Ports
	The ports are useful as you can just unplug a device that is not used and plug in another device in that port. The ports have different shapes and sizes that make it easy to connect devices to the system, as you cannot insert a plug in the wrong port. For example, you cannot insert the mouse plug in the printer port. The ports also have a symbol besides them to enable you to identify the port. Table 10.1 lists the commonly used symbols and the port name.
	Symbol Port
	Serial/COM Parallel USB IEEE 1394/Firewire PS/2 - Keyboard PS/2 - Mouse Line In Line Out Microphone Joystick
	Port Symbols
	_ Some symbols may differ on some systems.
10.2 Types of Ports
	The ports have different shapes and sizes, thus before purchasing a device you must check if you can attach the device to the system using the port available on the system. You must not force a device plug into a port or you may bend the pins. Some devices such as the keyboard and the mouse port on newer systems use the PS/2 ports that look the same but can be differentiated using the port color.
	10.2.1 Serial Ports
	A serial port is like a single lane road that sends and receives one bit of data at a time. Thus, the eight bits of data in one byte travel one bit at a time, one behind the other. The serial port connector also known as the Communication or COM port can have 9 or 25 pins. A serial port is used to connect devices such as the mouse and modems to the system.
	10.2.2 Parallel Ports
	The parallel port is like an eight lane road that transmits eight bits of data at a time. It is like eight cars moving on a wide road side by side. The parallel port connector has 25 pins to connect devices such as printers, scanners, external hard drives, and tape backup devices. The parallel port appears.
	25 Pin Parallel Port
	The different parallel ports are : _ Unidirectional - Transmits data in one direction at a time such that they can only send or receive data _ Standard Parallel Port (SPP) - Enables bidirectional data communication between the system and the device _ Enhanced Parallel Port (EPP) - Provides data transfer speed of 500 Kb to 2 Mb of data per second between the system and the device. This port is used for attaching external storage devices to the system such as an Iomega Zip drive. _ Enhanced Capabilities Port (ECP) - Provides increased data communication speed between the system and the printer
	10.2.3 DIN 5 Port
	The DIN 5 port is used to connect the keyboard to the system. This port is also called the AT port and uses 5 pins for connecting the keyboard and appears.
	10.2.4 PS/2 Port
	The PS/2 port is used to connect the keyboard and mouse to the system. The ports are available in a color that matches the color of the plug connecting the mouse and keyboard. This port uses 6 pins to connect the device and appears.
	10.2.5 Universal Serial Bus (USB) Ports
	The USB port is a rectangular port that is used to connect a variety of devices to the system. The USB port also supplies power to the device such as the web camera, if the device does not use an external power source. To use the USB device you must just plug the device into the USB port, as most USB devices offer Plug-and-Play support. However, you must install the USB driver before using the USB port.
	USB Port
	You can connect upto 127 devices to the system using the USB port using a USB hub. The device and the system connected using the USB can be at a maximum of 30 meters, thus you can connect 5 hubs to the USB.
	USB Hub
	The USB cable connects the system to the device and can have a maximum length of 5 meters, as the USB cable design does not support it due to electromagnetic fields. The USB cable has two different connections - one at each end of the USB cable, connection A and B. Connection A connects to the system and appears.
	USB Connection A
	Connection B is used to connect the USB cable to the device. Devices that have the USB cable built into them do not have this connection.
	USB Connection B
	The USB port is available in different versions having the same port shape. The different versions of USB ports available are: _ USB version 1.0 - Provides data transfer speed of 1.5 Mega bits per second _ USB version 1.1 - Removes bugs from USB version 1.0 _ USB version 2.0 - Provides data transfer speed of 10 Mega bits per second The USB port enables you to connect devices such as mouse, printers, scanners, digital cameras, modems, and speakers.
	10.2.6 Infrared Ports
	Devices use the infrared ports to communicate with the system without using wires. The devices send out infrared signals that enter the system through this port. The infrared port appears.
10.3 Working with the IEEE 1394 Bus
	The Institute of Electrical & Electronics Engineers (IEEE) 1394 is a standard for the external bus that enables fast and high data transfer between the system and the connected devices. The IEEE 1394 can transfer data at the speed of about 400 MB per second. The port using the IEEE 1394 standard appears.
	IEEE 1394
	The IEEE 1394 port can be used on Windows 98 Second Edition, Windows 2000, Windows XP, and Windows ME. This IEEE 1394 bus is used to connect and can also supply power to a wide range of devices to the system such as printers, scanners, web cameras and is generally used for transferring Audio and Visual data from a camera to the system. _ Apple uses the name FireWire and Sony uses i.Link for the IEEE 1394 port. Most manufacturers also refer to this port using the name of the standard, IEEE 1394. Infrared Port
	Best practices
	1. Check the hardware for any damage after unpacking it. 2. Write the details mentioned on the label of the hardware such as the model number, and the serial number, in a safe place such as a diary. 3. Read the documentation supplied with the hardware thoroughly. 4. Check if there is an empty expansion slot on the motherboard to install the IEEE 1394 card.
	Precautions
	1. Wear an antistatic wristband. 2. Ensure that the power supply is switched off before installing or uninstalling any hardware.
	Hands on exercise
	To install the IEEE 1394 card : 1. Open the system. 2. Locate the vacant expansion slot where the IEEE 1394 card must be installed. 3. Unscrew and remove the metal insert from the system case. 4. Insert the IEEE 1394 card in the expansion slot using a little force and taking care not to damage the motherboard. 5. Screw the IEEE 1394 card to the system case. 6. Close the system. 7. Start the system. 8. Install the IEEE 1394 drivers.
10.4 Configuring Ports with Interrupt Request (IRQ)
	Configuring IRQ line enables you to set the IRQ line number for the hardware device. The devices use the IRQ line to communicate with the microprocessor. The different IRQ line and their use are listed in Table 10.2:
	IRQ Typical Use Number
	0 System timer 1 Keyboard 2 Interrupt for IRQs 8-15 3 Second serial port (COM2) 4 First serial port (COM1) 5 Sound card 6 Floppy disk controller 7 First parallel port. Used by the printer or any device using the parallel port. 8 Real-time clock 9 Open interrupt 10 Open interrupt 11 Open interrupt 12 PS/2 mouse/Network Card 13 Floating point unit/coprocessor. Only used for internal signaling. 14 Primary IDE channel 15 Secondary IDE channel
	Table 10.2 - IRQ Lines
	There are 16 IRQ lines that the system uses for the device to communicate with the system. A device may be configured by the factory settings or manually to use an IRQ line that is already used by another device. If both these devices are used simultaneously, it will result in an IRQ line conflict and the system or the device may malfunction. To avoid this sharing conflict, it is advisable to set the devices such that you will only use one of the two devices sharing the same IRQ line at a time.
	Best practice
	It is preferred to allow Windows to automatically assign the IRQ line to avoid conflicts.
	Hands on exercise
	To change the IRQ line assigned to a device : _ You need administrator privileges to change the hardware settings. 1. Select Start _ Settings _ Control Panel. The Control Panel Window appears
	Control Panel Window
	2. Double-click the System icon. The System Properties sheet appears.
	System Properties Sheet
	3. Click the Hardware tab. The Hardware tab appears.
	Displaying the Hardware Tab
	4. Click Device Manager. The Device Manager showing the different devices appears
	Displaying the Device Manager
	5. Click the plus symbol to expand and display the different devices listed under an item. 6. Select a device such as Communications Port (COM1) under Ports (COM & LPT). 7. Right-click to see the popup menu. 8. Select Properties from the popup menu. The device properties sheet appears
	Displaying Device Properties Sheet
	9. Click the Resource tab. The Resource tab appears.
	Displaying Resource Tab
	10. Clear the Use automatic settings check box. 11. Double-click Interrupt Request from the Resource Settings list. The Edit Interrupt Request dialog box appears
	Edit Interrupt Request Dialog Box
	12. Choose the IRQ line number that does not conflict with any device from the Value spin box and click OK.
10.5 Troubleshooting
	Problems with the I/O ports cause errors to be displayed while using the device. The operating system may crash while using the device. The device may also not function if the device IRQ line conflicts with another device.
	10.5.1 Device not Working Properly
	A hardware device may not work if there is some problem with the I/O port, the system or with the device itself. To solve the problem of the device that is not working : 1. Check if the device is properly connected to the port. 2. Remove the device from the port and connect it to another vacant port. 3. Scan the system for viruses. 4. Uninstall and reinstall the device drivers. 5. Check if the card for the port is properly attached to the motherboard. 6. Try attaching the device to a different system to check if the device is functioning properly, if the device works on the other system then the port is spoilt. 7. Troubleshoot the device.
	10.5.2 IRQ Conflict
	IRQ conflicts occur when two hardware devices use the same IRQ line. When a conflict occurs the system displays an error and either one or both the hardware devices may not work. Your system may also hang or display an error message while using the conflicting device. You must identify the hardware that is causing the problem and change the IRQ of the conflicting device. To resolve the IRQ conflict : 1. Try to identify the hardware device that is causing the conflict. 2. Remove any new hardware installed, to check if the new hardware is causing the conflict. 3. Re-install the device driver. 4. Remove the card that the conflicting device uses, from the current expansion slot and install it in another free expansion slot. 5. Identify the conflicting device using the Device properties sheet, from the Device manager. Change the IRQ line of the conflicting device and click OK.
	Displaying Conflicting Device
	Conflicting Device