Input Devices - Upgrading and Repairing PCs - page 765

to your computer. Extension cables can be used if necessary to extend the distance.
After the mouse is connected to your computer, it communicates with your system through the use of a
device driver, which can be loaded explicitly or built into the OS software. The standard mouse
drivers in Windows are designed for the traditional two-button mouse or scroll mouse (in Windows
Me or later), but increasing numbers of mice feature additional buttons, toggles, or wheels to make
them more useful. These additional features require special mouse driver software supplied by the
manufacturer.
Pointing Device Interface Types
The connector that attaches your mouse to the system depends on the type of interface you are using.
Mice are most commonly connected to your computer through the following interfaces:
• Serial interface (obsolete)
• PS/2 mouse port
• USB port
• Bluetooth/wireless (transceiver connected via USB)
A fifth type of connection, the bus mouse (referred to by Microsoft as the InPort mouse), used a
dedicated ISA bus adapter card and is long obsolete.
Serial
A popular method of connecting a mouse to older PCs is through the standard serial interface. As with
other serial devices, the connector on the end of the mouse cable is typically a 9-pin female
connector; some old mice used a 25-pin female connector. Only a couple of pins in the DB-9 or DB-
25 connector are used for communications between the mouse and the device driver, but the mouse
connector typically has all 9 or 25 pins present.
Because most older PCs come with two serial ports, a serial mouse can be plugged into either COM1
or COM2. The device driver, when initializing, searches the ports to determine to which one the
mouse is connected. A few mouse drivers can't function if the serial port is set to COM3 or COM4,
but most can work with any COM port (1-4).
Because a serial mouse does not connect to the system directly, it does not use system resources by
itself. Instead, the resources are those used by the serial port to which it is connected. For example, if
you have a mouse connected to COM2, and if COM2 is using the default IRQ and I/O port address
range, both the serial port and the mouse connected to it use IRQ3 and I/O port addresses 2F8h-2FFh.
See the Chapter 14 section, “ Serial Ports , ” p. 730 .
PS/2 Mouse Port (PS/2)
Many motherboards include a PS/2 mouse port built into the motherboard. This port was introduced
by IBM on its PS/2 systems in 1987. Since then this interface has been called a PS/2 mouse port .
From a hardware perspective, a PS/2 mouse port is the same as the mini-DIN PS/2 keyboard port. In
fact, the PS/2 mouse port is connected to the 8042-type keyboard controller found on the
motherboard. PS/2 ports transfer data serially 1 bit at a time at a nominal rate of 12.5Kbps. Figure
15.12 shows a PS/2 mouse port connector.