Hardware Reference
In-Depth Information
2 PC expansion bus systems
The availability of a variety of standard expansion bus systems within the PC
environment must surely be the single most crucial factor in harnessing the
power of the machine. Having decided upon the platform for your application,
whether it be a conventional PC, an industrial PC, or some form of embedded
PC controller, there is a need to find an effective means of connecting your
hardware via an appropriate interface.
For many applications the internally available expansion (ISA/EISA, PCI,
or PCI-X) provides a means of connecting a wide range of external hardware
devices. Happily, a large number of manufacturers have recognized this fact
and have developed expansion cards specifically for control, data acquisition,
and instrumentation applications. For other applications it may be necessary
to make use of an interface to an external bus via the USB, serial, or parallel
ports. Alternatively, specialized PC controller/bus standards (such as PC/104)
may be appropriate. This chapter discusses a variety of different solutions to
the problem of connecting a PC to external hardware.
Expansion methods
PC expansion can be readily achieved by means of cards connected to the PC
bus by any one or more of the following general methods:
•
connectors available on the system motherboard (e.g. ISA/EISA, PCI, or
PCI-X);
•
an external
backplane bus
or a
stacking bus
system (e.g. PC/104 and PC/104-
Plus);
•
a high-speed serial interface to the external hardware (e.g. USB);
•
serial and/or parallel ports available on the motherboard.
The first two of these methods provide a more direct route to the system bus
which is based on connection to the motherboard bus signals. The second
two methods are less direct and may require substantial buffering as well as
serial-to-parallel conversion before external data can reach the system bus.
Development of PC
expansion bus
architectures
The signals present on an expansion bus can be divided into the following
general categories:
•
Address bus lines
•
Data bus lines
•
Read and write control signals
•
Interrupt request signals
•
DMA request and DMA acknowledge signals
•
Miscellaneous control signals
•
Clock signals
•
Power rails.
