External I/O Devices and Printers

ATTACHING I/O DEVICES

Various system resources are needed to install and support external devices, we’ll explain how the operating system communicates with devices. You’ll learn how to install a new device on a PC and how to resolve conflicts that are caused when two devices request the same system resources. In addition to the standard legacy system ports, you’ll also learn about USB and FireWire/iLink ports, which allow a variety of devices to be easily connected to your PC.

Fundamentals of Peripheral Installations

Added peripherals need a device driver or BIOS system resources, which may include an interrupt request number (IRQ), direct memory access channel (DMA channel), input/ output addresses (I/O addresses), upper memory addresses, and application software.

Software has many different levels, including device drivers that interface with the hardware and application software that interfaces with the drivers.

When several peripheral devices are added to a system, they might try to use the same resources, which could cause peripherals not to work. When two devices try to use the same IRQ, DMA channel, I/O address, or upper memory addresses, it usually causes problems.

Some peripherals are internal, meaning that they’re installed inside the computer case. Internal peripherals include optical drives and Zip drives, along with cards to support audio, video, and communications. External peripherals include printers, plotters, scanners, projectors, cameras, building environmental controls, lighting, security systems, and a host of others.

There are three basic steps for adding peripherals to a PC: (1) plug in the device, (2) install drivers, and (3) install application software.

Embedded BIOS on Devices

Some peripheral devices require several levels of software. Some external devices store needed software in their own cabinet, on a ROM chip, or a ROM chip on the interface board. This is called firmware or BIOS. Some peripheral devices designed for use on a wide variety of systems contain RAM for temporary storage of data. The technique varies with devices and can include flipping DIP switches, moving jumpers, and in most cases, using programs provided by the device manufacturer. Rarely, it’s necessary during installation to interface with the BIOS to set an IRQ number or I/O addresses. 

In some cases, system BIOS as well as device BIOS may come into play. BIOS on the hard drive manages access to the hard drive, while system BIOS on the system board manages communication between the hard-drive BIOS and the operating system (OS).

Device Drivers

Peripherals require device drivers. The two common types of drivers since Windows Vista was released are 32-bit and 64-bit. Windows uses 32-bit drivers natively, unless you’re using a 64-bit version of Windows.

Windows 32-Bit and 64-Bit Drivers 

Unlike previous versions, Windows XP and later doesn’t need to load drivers in specific startup files, because all common drivers are pre-loaded in the operating system. Booting the system with the device plugged in tells Windows to activate the driver. Windows drivers can be activated when a device is used and deactivated when not used to conserve memory.

Most extra Windows drivers come as part of a hardware package on a CD when you purchase a device. Windows and some device manufacturers offer the latest revisions to drivers on their Web sites. Windows allows you to view and change device drivers from the Control Panel. In Windows 7, for example, click on Start, then Control Panel. Then click on Display and click Adjust Resolution to view the currently installed display driver.

To change the driver, click on Advanced Settings, the Adapter tab, the Properties button, the Driver tab, and then the Update Driver button. The Update Device Driver Wizard will appear.

You can search manually for supported drivers or let Windows search for you. If you have a driver from a device that’s not supported by Windows, perform the search manually by selecting Browse my computer for driver software. Click Let me pick from a list to be able to add the driver from a CD, DVD, or a downloaded folder on the hard drive, as shown in Figures 3 and 4.

Always use 32-bit drivers with 32-bit Windows systems and

64-bit drivers with 64-bit Windows systems. While 64-bit Windows versions can use 32-bit drivers, performance will decrease.

Application Software

Most devices include basic application software so they can be used as soon as they’re installed. For example, a scanner will usually include software to scan and manipulate images and documents. Advanced application software can be purchased to replace the basic software included with the device and provide more function.

Ports and Expansion Slots         

There are several ways that devices can connect to a PC. The following is a preview of the topics we’ll discuss for connecting devices to your computer.

Most computers come with serial, parallel, USB, and sometimes FireWire/iLink ports mounted on the system board. On older systems, an I/O controller card in an expansion slot provided serial and parallel ports.

Using PCI Expansion Slots

PCI and PCI-Express are local buses that run in sync with the CPU. PCI-Express slots are often colored yellow so they can be easily distinguished from the PCI expansion slots, which are usually white or green. The picture below shows the PCI-Express X16 and X1 slots on a system board for comparison.

Because the PCI-Express bus is faster than the PCI bus, PCI-Express slots are often used for fast I/O devices such as network cards or graphics adapters. When installing either a PCI or PCI-Express card, it’s unlikely you’ll need to configure the IRQ or I/O address because the startup PnP BIOS and on-board bus controller do this for you.

Use the Device Manager to see which IRQ has been assigned to a PCI device. Go to Settings and click on Control Panel. Click on the System icon to bring up the System Properties window. Select the Device Manager link. Now, suppose your PC has a PCI video card. Clicking the next to “Display adapters” will yield the name of this video card. Double-click on the device to bring up its Resources window; here you can find which IRQ (09, 10, 11) has been assigned to the device.

PCI Bus IRQ Steering

Starting with PCI 2.1, PCI and PCI-Express both utilize PCI bus IRQ steering, making it possible for PCI devices to share an IRQ. By using PCI bus IRQ steering, Windows can automatically assign or “steer” the PCI bus’ IRQs. All versions of Windows from XP forward support IRQ steering.

Sometimes an IRQ conflict can happen when the startup

BIOS isn’t aware that a legacy device is using a particular IRQ and assigns that IRQ to the PCI or PCI-Express bus, which then assigns it to a specific device. With IRQ steering, Windows can sometimes solve the problem by reassigning another IRQ to the bus to allow the legacy device to be the sole owner of its IRQ.

For this to happen, Windows must detect an unused IRQ and assign it as a substitution. It then reserves this IRQ for PCI or PCI-Express use. The word “Holder” indicates an IRQ is reserved.

IRQ steering can also cause a problem. If Windows puts a holder on an IRQ, this might cause the device using it to have problems. Also, if two devices are having conflicts, sometimes IRQ steering can mask the problem, making it difficult to diagnose. IRQ steering can erroneously put a holder on an IRQ that’s being used by a legacy device. 

When Device Installations Create Problems

Suppose you install a new sound card and it doesn’t work. You also notice your network card has stopped communicating. Poor cable or card connections can cause these symptoms. Check all connections, then remove the sound card and see if the network card starts working again.

Device documentation is the best place to begin diagnosing device installation problems. 

Using Serial Ports

Serial ports are always male ports on the computer and use DB-9 or DB-25 connectors. DB stands for data bus, and the number 9 or 25 indicates the number of pins.

Designers designated COM1, COM2, COM3, and COM4 as serial ports to simplify allocation of system resources. COM assignments represent a designated IRQ and I/O address.

Serial ports are physical connections. COM assignments are logical connections. Saying COM1 is the same thing as saying IRQ4 and I/O address 03F8.

Configuring an I/O card with a serial port COM assignment usually requires the arrangement of jumpers on the card. CMOS is most often used for COM assignments of ports connected directly to the system board. Sometimes the setup screen shows COM assignments, and sometimes it shows the IRQ and I/O address.

A serial port conforms to the standard interface called

RS-232 (Reference Standard 232). Sometimes written RS-232b or RS-232c, the lower-case “b” or “c” represents the revision level. Even though serial ports are available in 9 and 25-pin configurations, only nine of the pins are used. Adapters are available on the market to convert the ports to suit whatever serial cables you happen to be using.

Using Parallel Ports

Typically, there are three types of printer ports:

•     SPP—Standard parallel port

•     EPP—Enhanced parallel port

•     ECP—Extended-capabilities parallel port

The SPP is often referred to as a Centronics port or normal parallel port. The name “Centronics” is taken from the 36-pin connection used for printers.

A standard parallel port allows data flow in only one direction. The EPP and ECP are both bidirectional. The extended-capabilities parallel port uses Direct Memory Access (DMA).

Cable length can be critical in parallel port connections. Ten feet is normally satisfactory, but you should never exceed fifteen feet.

When configuring parallel ports it’s important to read the documentation provided with the I/O card. If the port is connected directly to the system board, look at CMOS setup to configure the port.

SCSI Devices

Installing a SCSI device is normally done one of two ways:

1.   Install the SCSI device using a simplified version of a SCSI host adapter designed to accommodate one or two devices. These adapters often come bundled in the SCSI device package.

2.   Install the SCSI device on an existing or new host adapter designed to handle several devices.

Matching the Host Adapter to SCSI Devices

When matching a host adapter or determining if an existing host adapter will work with a new SCSI device, consider the following:

•     Legacy SCSI standards include SCSI-1, SCSI-2, SCSI-3,and Fast SCSI. Current SCSI standards include Wide Ultra 2 SCSI, Ultra 160 SCSI, Ultra 320 SCSI, and Ultra 640 SCSI.

•     SCSI-1, SCSI-2, and Fast SCSI use 50-pin connectors.

•     Wide SCSIs use 68-pin connectors, while Ultra SCSIs use 68 or 80-pin connectors. 

A SCSI device must match the host adapter based on the number of pins on the connectors and compatibility standards between the host adapter and the device.

The host adapter must fit the expansion slot you plan to use. SCSI host adapters come in either PCI or PCI-Express bus. For faster data transfer rate, it’s better to use the PCI-Express bus.  

Choose a host adapter that uses bus mastering. Buses that support bus mastering don’t require a DMA channel for the SCSI host adapter.

The ASPI or CAM standard also affects the way the host adapter relates to the OS. Many host adapters provide their own host adapter drivers to be used by the OS. Manufacturers of host adapters usually provide the drivers on a CD-ROM. Select a host adapter that matches the device according to its electronic signaling method. The cable choices are single-ended and differential. Don’t mix the two, or you could damage the devices.  Host adapters are available that allow you use 50-pin and 68-pin connectors along with several standards that allow you to choose a variety of devices without the need for a second adapter. Select a host adapter that supports one of the leading driver standards: Advanced SCSI Programming Interface (ASPI) or Common Access Method (CAM). Be sure the host adapter and all device drivers meet the same standard.  Bus mastering is a feature supported by some bus architectures that enables a controller connected to the bus to communicate directly with other devices on the bus without going through the CPU. Most modern bus architectures, including PCI, support bus mastering because it improves performance. Using USB Ports Using Universal Serial Bus (USB) ports is less complicated than using parallel or serial ports. The OS, together with the USB host controller, manages the USB port resources. Like the SCSI bus we just discussed, all ports and devices on the universal serial bus use only one IRQ, I/O address, and DMA channel.  Most system boards have two or more USB ports. Expansion cards with USB ports are available for older systems. To install a USB device you’ll need  A USB port or expansion card with USB USB Host (Bus Master) port and USB firmware.  A USB device driver.       USB Device channel are needed for a USB host controller to manage multiple devices. Use the following general steps to install a USB device. 1.   Using the Device Manager, verify that the USB host controller driver is installed (Figure 10). If the controller isn’t installed, install it from the Control Panel by double clicking the Devices and Printers icon. If you have trouble installing the controller, verify that support for USB is enabled. 2.   Plug in the USB device and install its device driver. For example, if installing a scanner, insert the CD that came with the scanner in the optical drive and enter D:\Setup.exe in the Run dialog box. Follow the screen prompts, if any, to complete installation. Verify that Windows sees the device in the Device Manager with no conflicts and without errors. 3.   Install the application software to use the device. Conduct a test operation of the device to confirm that everything is functioning properly. Using Device Manager, verify that the USB host controller is installed. Using FireWire/iLink Ports FireWire/iLink ports are becoming standard on all new system boards There are three types of FireWire/ iLink connectors: a 4-pin connector that doesn’t supply voltage to the device, and 6-pin and 9-pin connectors that do supply voltage. FireWire/iLink uses isochronous data transfer, meaning that data is transferred continuously within time constraints. This works well for real-time data like motion camera monitoring. Because data can be transferred from one device to another without involving the CPU, it’s an ideal medium for consumer electronics products like VCRs, DVDs, TVs, and digital cameras. A user could record a home movie with a digital camcorder, then download the data through a digital VCR to a FireWire/iLink–compliant hard drive. The PC can later read the data from the hard drive and use it as input to video-editing application software. If the digital camcorder is FireWire/ iLink (IEEE 1394) compliant, it can download the data directly to the PC. IEEE 1394.A (the “A” is the revision level) is a FireWire/iLink standard that supports speeds of 100, 200, or 400 Mbps. It allows cable lengths up to 4.5 meters (a little more than 14½ feet) and is hot-pluggable. IEEE 1394.B supports speeds between 800 Mbps and 3.2 Gbps, and cable lengths of up to 100 meters, or more than 300 feet.

To use a FireWire/iLink port, follow these steps:

1.   Verify that Windows recognizes that a FireWire/iLink controller is present on the system board. Using the Device Manager, look for the FireWire/iLink Bus Controller listed as an installed device. Click the c beside the controller in the Device Manager to see the

specific brand of FireWire/iLink controller the board contains. If the controller isn’t installed or isn’t working, reinstall the driver. In the Control Panel window, double click the Devices and Printers icon. If you have problems installing the driver, verify that FireWire/iLink support is enabled.

2.   Plug the device into the FireWire/iLink port. Install the device driver for the device. For example, for a Sony camcorder, insert the CD that contains the supporting software into the optical drive and follow the Auto-Play prompts to install the software. If the disc doesn’t auto-start, click Start and type <drive>:\Setup.exe in the Search programs and files field, where <drive> is the drive letter of your optical drive. When the device is plugged in and the drivers are installed, you should see the device listed in the Device Manager under Sound, Video and Game Controllers. If you don’t see it, turn the camcorder off and then back on.

3.   Install the application software to use the device. Conduct a test operation of the device to confirm everything is functioning properly.

For system boards that don’t support FireWire/iLink, you can install a FireWire/iLink host adapter.