Hardware Reference
In-Depth Information
keyboard and installs operating systems knows; if the operating system has
not been instructed to load a keymap, then the system defaults to QWERTY:
the standard U.S. keyboard. This is something to remember.
The traditional PC keyboard is long dead; manufacturers are making friendlier
keyboards with added buttons to control volume, applications, or even some
laptop functions. More advanced keyboards have programmable buttons that
can either be simple scancodes or preprogrammed to write several scancodes at
once to the computer. Even more advanced gaming keyboards also have LCD
screens and sometimes LCD keys. These are not “standard” keyboards; they
require specii c drivers to function but still embed part of a standard keyboard.
When entering the BIOS, these special keyboards still work, but the LCD screen
doesn't. To achieve this, there is often a small USB hub inside, with different
components behind the hub: the keyboard, the LCD screen, and sometimes
external USB ports to connect USB keys, headphones, and so on.
Mice
Mice are, today, a basic component of every computer, but it wasn't always the
case. Early computers did not have a mouse, and they were added only when
graphical interfaces became standard.
A mouse is a device, either mechanical or optical, that senses movement rela-
tive to the surface on which it is placed and sends movement information to
the computer in
x
-/
y
-coordinates. In addition, there are also buttons (typically
left, middle, and right), with a middle button often capable of scrolling. More
advanced mice may have several more buttons, and gaming mice often have
10 or more buttons.
Hubs
USB hubs work like network hubs; they enable you to connect several devices
onto a single port. To do this, the hub connects to the computer's USB host, and
further devices are placed behind the hub. The hub dispatches messages from
the host to the device, and messages from devices are sent to the host.
Arduino Due
The Arduino Due is different from other Arduinos for several reasons. It is
based on Atmel's SAM3X8E microcontroller, which is in turn based on an ARM
Cortex-M3, a powerful device. It has two micro-USB connectors, and runs at
3.3 V (see Figure 20-1).
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