Hardware Reference
In-Depth Information
Caution
I have also seen PCs with external power supplies that used the same or similar mini-DIN
connectors to attach the power supply. Although cross-connecting the mini-DIN connectors
of a mouse and keyboard is a harmless annoyance, connecting a power supply to a keyboard
socket would be disastrous.
USB keyboards use the Series A USB connector to attach to the USB port built into mod-
ern computers. For more information on USB, refer to
Chapter 14
,
“
External I/O Inter-
USB Keyboards
Mostkeyboards nowonthe market connect tothe PCvia aUSBportinstead ofthe stand-
ardPS/2keyboardport.BecauseUSBisauniversalbusthatusesahubtoenablemultiple
devices to connect to a single port, a single USB port in a system can replace the stand-
ard serial and parallel ports as well as the keyboard and mouse ports. Many systems and
motherboards still include the standard PS/2 keyboard and mouse ports (now called
leg-
acy
ports) as well as USB, but many newer
legacy-free
systems and replacement mother-
boards have only USB ports for interfacing external devices.
Most keyboard manufacturers now market USB keyboards, but if you want to use your
keyboardwithbothlegacy(PS/2)andlegacy-free(USB)systems,themosteconomicway
to do so is to specify a keyboard that includes both a USB connector and an adapter to
permit the keyboard to work with PS/2 ports.
Although rare in modern systems, some older systems don't accept USB keyboards, even
those with USB ports, because the standard PC BIOS has a keyboard driver that expects
a standard keyboard port interface to be present. When a USB keyboard is installed on a
system that lacks USB keyboard support, the system can't use it because no driver exists
in the BIOS to make it work. In fact, some systems see the lack of a standard keyboard as
an error and halt the boot process until one is installed.
To use a keyboard connected via the USB port, you must meet three requirements:
• Have a USB port in the system.
• Run Microsoft Windows 98 or newer. (Previous versions did not include USB key-
board drivers.)
•Have a system chipset and BIOS that feature USB Legacy (keyboard and mouse) sup-
port.
USB Legacy support means your motherboard has a chipset and ROM BIOS drivers that
enable a USB keyboard to be used outside the Windows graphical user interface (GUI)
