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Hardware Configuration Features: Dell Precision™ WorkStation 420 Systems User's Guide

	Overview		I/O Ports and Connectors
	Jumpers		Interrupt Assignments
	System Board Labels		Memory Allocations

Overview

This section provides specific information about the jumpers on your system board and the input/output (I/O) ports and connectors on the back panel of your computer. It also provides some basic information on jumpers, a listing of interrupt request (IRQ) assignments, and memory maps.

Jumpers

Jumpers provide a convenient and reversible way of reconfiguring the circuitry on a printed circuit board. When you reconfigure your system, you may need to change jumper settings on your system board; you may also need to change jumper settings on expansion cards or drives.

Jumpers are small blocks on a circuit board with two or more pins emerging from them (see Figure 1). Plastic plugs containing a wire fit down over the pins. The wire connects the pins and creates a circuit.

Figure 1. Jumpers

To change a jumper setting, pull the plug off its pin(s) and carefully fit it down onto the pin(s) indicated.

NOTICE: Make sure that your system is turned off before you change a jumper setting. Otherwise, damage to your system or unpredictable results may occur.

A jumper is referred to as open or unjumpered when the plug is pushed down over only one pin or if there is no plug at all. When the plug is pushed down over two pins, the jumper is referred to as jumpered. The jumper setting is often shown in text as two numbers, such as 1-2. The number 1 is printed on the circuit board so that you can identify each pin number based on the location of pin 1.

Figure 2 shows the location and default settings of the jumper blocks on your system board. See Table 1 for the designations, default settings, and functions of your system's jumpers.

Figure 2. System Board Jumpers

Table 1. System Board Jumpers Settings

Jumper	Setting	Description
RTCRST		Real-time clock and CMOS reset. Install a jumper plug on these pins for approximately 1 second to reset the contents of the real-time clock and the CMOS. Do not leave the jumper plug installed.
PSWD		Password features enabled. Password features disabled.
NOTE: For the full name of an abbreviation or acronym used in this table, see the Glossary.

System Board Labels

Table 2 lists the labels for connectors and sockets on your system board and control panel and gives a brief description of their functions.

Table 2. System Board and Control Panel Connectors and Sockets

I/O Ports and Connectors

The I/O ports and connectors on the back panel of your computer are the gateways through which your computer system communicates with external devices, such as a keyboard, mouse, printer, and monitor. Figure 3 identifies the I/O ports and connectors for your computer.

Figure 3. I/O Ports and Connectors

Serial and Parallel Ports Overview

The two built-in serial ports use 9-pin D-subminiature connectors on the back panel. These ports support devices such as external modems, printers, plotters, and mice that require serial data transmission (the transmission of data one bit at a time over one line).

Most software uses the term COM (for COMmunications) plus a number to designate a serial port (for example, COM1 or COM2). The default designations of your computer's integrated serial ports are COM1 and COM2.

The integrated parallel port uses a 25-pin D-subminiature connector on the computer's back panel. This I/O port sends data in parallel format (where eight data bits, or one byte, are sent simultaneously over eight separate lines in a single cable). The parallel port is used primarily for printers.

Most software uses the term LPT (for Line PrinTer) plus a number to designate a parallel port (for example, LPT1). The default designation of your computer's built-in parallel port is LPT1.

Port designations are used, for example, in software installation procedures that include a step in which you identify the port to which your printer is attached, thus telling your software where to send its output. (An incorrect designation prevents the printer from printing or causes scrambled print.)

Serial Port Connectors

If you reconfigure your hardware, you may need pin number and signal information for the serial port connectors. Figure 4 illustrates the pin numbers for the serial port connectors, and Table 3 lists and defines the pin assignments and interface signals for the serial port connectors.

Figure 4. Pin Numbers for the Serial Port Connectors

Table 3. Pin Assignments and Interface Signals for the Serial Port Connectors

Parallel Port Connector

If you reconfigure your hardware, you may need pin number and signal information for the parallel port connector. Figure 5 illustrates the pin numbers for the parallel port connector, and Table 4 lists and defines the pin assignments and interface signals for the parallel port connector.

Figure 5. Pin Numbers for the Parallel Port Connector

Table 4. Pin Assignments and Interface Signals for the Parallel Port Connector

External SCSI Connector

The 68-pin external small computer system interface (SCSI) connector on the system back panel supports external Ultra SCSI devices such as scanners, zip drives, and optical drives.

If you reconfigure your hardware, you may need pin number and signal information for the external SCSI connector. Figure 6 illustrates the pin numbers for the external SCSI connector, and Table 5 lists and defines the pin assignments and interface signals for the external SCSI connector.

Figure 6. Pin Numbers for the External SCSI Connector

Table 5. Pin Assignments and Interface Signals for the External SCSI Connector

Keyboard and Mouse Connectors Overview

Your system uses a Personal System/2 (PS/2)-style keyboard and supports a PS/2-compatible mouse. Cables from both devices attach to 6-pin miniature Deutsche Industrie Norm (DIN) connectors on the back panel of your computer.

A PS/2-compatible mouse works identically to an industry-standard serial mouse or bus mouse except that it has its own dedicated connector, which frees up both serial ports and does not require an expansion card. Circuitry inside the mouse detects either the movement of a small ball or the input from an optical sensor and relays the direction to the computer.

Mouse driver software can give the mouse priority with the microprocessor by issuing IRQ12 whenever a new mouse movement is made. The driver software also passes along the mouse data to the application program that is in control.

Keyboard Connector

If you reconfigure your hardware, you may need pin number and signal information for the keyboard connector. Figure 7 illustrates the pin numbers for the keyboard connector, and Table 6 lists and defines the pin assignments and interface signals for the keyboard connector.

Figure 7. Pin Numbers for the Keyboard Connector

Table 6. Pin Assignments and Interface Signals for the Keyboard Connector

Mouse Connector

If you reconfigure your hardware, you may need pin number and signal information for the mouse connector. Figure 8 illustrates the pin numbers for the mouse connector, and Table 7 lists and defines the pin assignments and interface signals for the mouse connector.

Figure 8. Pin Numbers for the Mouse Connector

Table 7. Pin Assignments and Interface Signals for the Mouse Connector

Video Connector

For information on your video connector, see the manufacturer's specifications that came with your video card.

NIC Connector

Your system contains an RJ45 connector (see Figure 9) on the back panel for attaching an unshielded twisted pair (UTP) Ethernet cable, which is used in 10BASE-T and 100BASE-TX networks. The network interface controller (NIC) provides all the functions normally handled by a separate network expansion card. To connect your system to and configure it for use on an Ethernet network, see "Using the Network Interface Controller."

Figure 9. NIC Connector

USB Connectors

Your system contains two Universal Serial Bus (USB) connectors for attaching USB-compliant devices. USB devices are typically peripherals such as keyboards, mice, printers, and computer speakers.

NOTICE: Do not attach a USB device or a combination of USB devices that draw a maximum current over 500 milliamperes (mA) per channel at +5 volts (V). Attaching devices that exceed this threshold may cause the USB ports to shut down. See the documentation that came with the USB devices for their maximum current ratings.

If you reconfigure your hardware, you may need pin number and signal information for the USB connectors. Figure 10 illustrates the pin numbers for the USB connectors, and Table 8 lists and defines the pin assignments and interface signals for the USB connectors.

Figure 10. Pin Numbers for the USB Connectors

Table 8. Pin Assignments and Interface Signals for the USB Connectors

Microphone Jack

You can use the microphone jack (see Figure 11) to attach a nondynamic monaural microphone for personal computers. Connect the audio cable from the microphone to the microphone jack. The microphone input is a mono source with maximum signal levels of 130 millivolts root mean squared (mVrms).

Figure 11. Microphone Jack

Line-Out Jack

You can use the line-out jack (see Figure12) to attach most computer speakers. The line-out jack is not amplified, so speakers with integrated amplifiers are required. Connect the audio cable from the speakers to this jack.

Figure 12. Line-Out Jack

Line-In Jack

You can use the line-in jack (see Figure 13) to attach record/playback devices such as cassette players, CD players, and VCRs. Connect the line-out cable from any of these devices to the line-in jack on the back of your computer.

Figure 13. Line-In Jack

Interrupt Assignments

Problems can arise if two devices attempt to use the same IRQ line. To avoid this type of conflict, check the documentation for the default IRQ line setting for each installed device. Then consult Table 9 to configure each device for one of the available IRQ or other lines.

NOTE: Interrupts for the integrated sound, NIC, and both SCSI channels are assigned dynamically by the system basic input/output system (BIOS).

Table 9. Interrupt Assignments

Memory Allocations

Programs operating under MS-DOS� (real-mode operation) can address only 1 megabyte (MB) (1024 kilobytes [KB]) of system memory. This area is divided into conventional memory (sometimes called base memory) and upper memory. All system memory above this 1 MB is called extended memory and cannot be directly addressed by MS-DOS-based programs without the aid of memory-managing software as found in Microsoft� Windows� 98 or Windows NT�.

Table 10 provides a map of the conventional memory area. When the microprocessor or a program addresses a location within the conventional memory range, it is physically addressing a location in main memory, which is the only main memory it can address under MS-DOS.

Table 10. Conventional Memory Map

Table 11 provides a map of the upper memory area. Some of these addresses are dedicated to various system devices, such as the system BIOS. Others are available for use by expansion cards and/or an expanded memory manager (EMM). When the microprocessor or a program addresses a location within the upper memory area, it is physically addressing a location within one of these devices.

Table 11. Upper Memory Map

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