Hardware Reference
In-Depth Information
Figure 12.1
Three basic approaches to PC-based instruments: (a) internally
fitted PC expansion cards; (b) PC expansion cards in an external card frame;
and (c) separately enclosed PC instruments linked via a parallel port,
RS-232 serial port, USB, or via the IEEE-488 bus
fitting and, since there may be a limited number of slots available, the expansion
capability may be somewhat limited.
An external rack system allows the PC bus to be extended so that standard
PC expansion cards may be fitted into an external card frame. This system is,
however, relatively expensive and generally only appropriate where large-scale
expansion is required. An alternative to that of extending the PC bus beyond
the confines of the system enclosure is that of making use of a proprietary I/O
bus. Such systems generally provide for between 1 and 32 I/O boards mounted
in standard rack enclosures.
Separately enclosed modules (which may be interfaced to a PC by means
or
the
RS-232,
USB,
or
IEEE-488
bus)
provide
the
third
of
this
trio
of
