Hardware Reference
In-Depth Information
flip-flops for memories with any word size desired. Memories are available as
RAM, ROM, PROM, EPROM, EEPROM, and flash. Static RAMs need not be
refreshed; they keep their stored values as long as the power remains on. Dynamic
RAMs, on the other hand, must be refreshed periodically to compensate for leak-
age from the little capacitors on the chip.
The components of a computer system are connected by buses. Many, but not
all, of the pins on a typical CPU chip directly drive one bus line. The bus lines can
be divided into address, data, and control lines. Synchronous buses are driven by a
master clock. Asynchronous buses use full handshaking to synchronize the slave
to the master.
The Core i7 is an example of a modern CPU. Modern systems using it have a
memory bus, a PCIe bus, and a USB bus. The PCIe interconnect is the dominant
way to connect the internal parts of a computer at high speeds. The ARM is also a
modern high-end CPU but is intended for embedded systems and mobile devices
where low power consumption is important. The Atmel ATmega168 is an example
of a low-priced chip good for small, inexpensive appliances and many other price-
sensitive applications.
Switches, lights, printers, and many other I/O devices can be interfaced to
computers using parallel I/O interfaces. These chips can be configured to be part
of the I/O space or the memory space, as needed. They can be fully decoded or
partially decoded, depending on the application.
PROBLEMS
1.
Analog circuits are subject to noise that can distort their output. Are digital circuits
immune to noise? Discuss your answer.
2.
A logician drives into a drive-in restaurant and says, ''I want a hamburger or a hot dog
and french fries.'' Unfortunately, the cook flunked out of sixth grade and does not
know (or care) whether ''and'' has precedence over ''or.'' As far as he is concerned,
one interpretation is as good as the other. Which of the following cases are valid inter-
pretations of the order? (Note that in English ''or'' means ''exclusive or.'')
a. Just a hamburger.
b. Just a hot dog.
c. Just french fries.
d. A hot dog and french fries.
e. A hamburger and french fries.
f. A hot dog and a hamburger.
g. All three.
h. Nothing—the logician goes hungry for being a wiseguy.
