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I/O Ports and Connectors

I/O Ports and Connectors
Serial and Parallel Ports
Keyboard and Mouse Connectors
Video Connector

This section provides specific information about the input/output (I/O) ports and connectors on the back panel of the computer system.

I/O Ports and Connectors

The I/O ports and connectors on the back panel of the system are the gateways through which the computer system communicates with external devices, such as a keyboard, mouse, printer, and monitor. Figure 1 identifies the I/O ports and connectors for your system.

Serial and Parallel Ports

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 system's built-in serial ports are COM1 and COM2. COM1 is the bottom connector; COM2 is on the top.

The built-in parallel port uses a 25-pin D-subminiature connector on the system'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 the system'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 a printer is attached, thus telling the software where to send its output. (An incorrect designation prevents the printer from printing or causes scrambled print.)

Figure 1. I/O Ports and Connectors

Adding an Expansion Card Containing Serial or Parallel Ports

The system has an autoconfiguration capabilityfor the serial ports. This feature lets you add an expansion card containing a serial port that has the same designation as one of the built-in ports, without having to reconfigure the card. When the system detects the duplicate serial port on the expansion card, it remaps (reassigns) the built-in port to the next available port designation.

Both the new and the remapped COM ports share the same interrupt request (IRQ) setting, as follows:

COM1, COM3: IRQ4 (shared setting)
COM2, COM4: IRQ3 (shared setting)

These COM ports have the following I/O address settings:

COM1: 3F8h
COM2: 2F8h
COM3: 3E8h
COM4: 2E8h

For example, if you add an internal modem card with a port configured as COM1, the system then sees logical COM1 as the address on the modem card. It automatically remaps the built-in serial port that was designated as COM1 to COM3, which shares the COM1 IRQ setting. (Note that when you have two COM ports sharing an IRQ setting, you can use either port as necessary but you may not be able to use them both at the same time.) If you install one or more expansion cards with serial ports designated as COM1 and COM3, the corresponding built-in serial port is disabled.

Before adding a card that remaps the COM ports, check the documentation that accompanied your software to make sure that the software can be mapped to the new COM port designation.

To avoid autoconfiguration, you may be able to reset jumpers on the expansion card so that the card's port designation changes to the next available COM number, leaving the designation for the built-in port as is. Alternatively, you can disable the built-in ports through the System Setup program. The documentation for your expansion card should provide the card's default I/O address and allowable IRQ settings. It should also provide instructions for readdressing the port and changing the IRQ setting, if necessary.

The built-in parallel port has autoconfiguration capability through the System Setup program; that is, if you set the parallel port to its automatic configuration and add an expansion card containing a port configured as LPT1 (IRQ7, I/O address 378h), the system automatically remaps the built-in parallel port to its secondary address (IRQ5, I/O address 278h). If the secondary port address is already being used, the built-in parallel port is turned off.

For general information on how your operating system handles serial and parallel ports, and for more detailed command procedures, see your operating system documentation.

Serial Port Connectors

If you reconfigure your hardware, you may need pin number and signal information for the serial port connectors. Figure 2 illustrates the pin numbers for the serial port connectors, and Table 1 lists and defines the pin assignments and interface signals for the serial port connectors.

Figure 2. Pin Numbers 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 3 illustrates the pin numbers for the parallel port connector, and Table 2 lists and defines the pin assignments and interface signals for the parallel port connector.

Figure 3. Pin Numbers for the Parallel Port Connector

Keyboard and Mouse Connectors

The 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 system. The keyboard connector is on the left; the mouse connector is on the right.

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 the movement of a small ball and relays the direction to the system.

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

Keyboard Connector

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

Figure 4. Pin Numbers for the Keyboard Connector

Mouse Connector

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

Figure 5. Pin Numbers for the Mouse Connector

Video Connector

The system uses a 15-pin high-density D-subminiature connector on the back panel for attaching a video graphics array (VGA)-compatible monitor to your system. The video circuitry on the system board synchronizes the signals that drive the red, green, and blue electron guns in the monitor.

NOTE: Installing a video card automatically disables the system's built-in video subsystem.

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

Figure 6. Video Connector Pins

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