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Unformatted text preview: es are listed. These show the entire range of I/O addresses for this device; the more complex the device, the more I/O addresses it uses. Address ranges are
generally referred to by the first value in the range, commonly known as the I/O base
NOTE All I/O addresses only use the last 16 bits (they all start with 0000).
Sixteen bits makes 216 = 65,536 I/O address rangesplenty for even the most
modern PCs. Should PCs begin to need more I/O addresses in the future, the
current I/O addressing system is ready.
Here are the most important items to remember about I/O addresses. First, every
device on your PC has an I/O address. Without it, the CPU wouldn’t have a way to send
a device commands. Second, I/O addresses are configured automatically: you just plug
in a device and it works. Third, no two devices should share I/O addresses. The system
handles configuration, so this happens automatically. Interrupt Requests
Between the standardized expansion bus connections and BIOS using I/O addressing,
the CPU can now communicate with all of the devices inside the computer, but a third
and final hurdle remains. I/O addressing enables the CPU to talk to devices, but how
does a device tell the CPU it needs attention? How does the mouse tell the CPU that
it has moved, for example, or how does the keyboard tell the CPU that somebody just
pressed the J key? The PC needs some kind of mechanism to tell the CPU to stop doing
whatever it is doing and talk to a particular device (Figure 8-16). This mechanism is
called interruption. Figure 8-16
How do devices
tell the CPU they
need attention? ch08.indd 303 12/14/09 2:49:24 PM All-In-One / CompTIA Network+ All-in-One Exam Guide / Meyers & Jernigan / 170133-8 / Chapter 8 CompTIA A+Certification All-in-One Exam Guide 304 Every CPU in the PC world has an INT
(interrupt) wire, shown in Figure 8-17. If
a device puts voltage on this wire, the CPU
stops what it’s doing and deals with the
interrupting device. Suppose you have a
PC with only one peripheral,...
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This note was uploaded on 04/27/2010 for the course COMPTIA 1201 taught by Professor N/a during the Spring '10 term at Galveston College.
- Spring '10