Computer Peripherals

Figure 1.1 Local bus
(v)
Random logic: For simple devices, random logic circuits may be used to check the
status registers, read and write the data registers, perform timing, handle interrupt
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Introduction
4
signals and other functions. However, an embedded micro controller chip is frequently
used.
0.4.
Interfacing to Input/Output Devices
Interfacing between a CPU and a peripheral usually involves a trade-off between hardware
and software. The advantage of hardware is speed, whereas the disadvantages are cost and
inflexibility. The advantage of software is versatility, whereas its main disadvantage is its slow
speed.
Interfacing can be handled entirely by the CPU (in software, with minimal hardware
support), or at the other extreme, by a dedicated (intelligent) peripheral controller (in hardware,
with minimal software support). Somewhere between these two extremes is the more usual master
(CPU)-to-slave (peripheral) configuration, where the (dumb) peripheral support chip has a
number of built-in functions, accessible by the CPU writing various bit patterns to its onboard
control (command) register(s). The peripheral support chip handles many of the tasks with which
the CPU would otherwise need to concern itself.
A recent trend has been the emergence of coprocessor peripheral support chips which
enable the CPU and coprocessor to carry out their respective tasks concurrently, communicating
with each other upon completion. In many cases, these coprocessors are so intelligent that their
processing ability rivals that of the host CPU. The resulting configuration more closely resembles
a multiprocessor or distributed processing system, rather than the more traditional CPU-support
chip master-slave relationship. For example, the PCI support chips that your have learned in
CE302.