Specifications

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3.350" with out using riser cards. There are two types of Low
Profile PCI boards: MD1 and MD2. Both are built on 32-bit
addressing, and differ only in length (MD1 being shorter than
MD2.) Systems can be designed to support one or both
configurations. Existing PCI backplanes used for standard cards
can also accept the Low Profile cards. However, the Low Profile
specification also includes a new bracket design that cannot be
used with standard PCI boards.
Mini PCI, on the other hand, is not backward compatible with
any older devices. It is designed to be used by system integrators
to add additional functionality for mobile computers. It requires
a completely new interface, and is typically used to add
communication peripherals such as modems and network interface
cards to notebook computers, docking stations, or sealed case
PCs.
Mini PCI boards are even smaller than Low Profile boards, with a
minimum size specification of 2.75" x 1.81" x 0.22." They are
functionally equivalent to standard and Low Profile boards, using
the same protocols, PC signals and software drivers. However,
because of the small size they require higher density, more
compact, and thus more expensive components. So, while Mini
PCI is extremely useful for the mobile applications for which it
was intended, it is not the most economical or flexible choice for
desktop expansion.
PCI for Data Communication
PCI is fast becoming the de facto standard for board-level
expansion slots in PC-based systems. However, for serial and
parallel communication, the potential of PCI goes largely
untapped. Limitations of these communication protocols
considerably slow down the system. (See pages 25-28 for more
on serial and parallel communication.) The PCI specification
anticipates this situation, and the bus is designed to slow down
when dealing with low speed devices. So, though running serial
and parallel devices via a PCI bus will not cause system problems,
neither will it significantly improve system performance over ISA.
But, as ISA slots are fast becoming obsolete, you may have no
choice but to use PCI add-in boards in newer systems. For
higher speed devices such as audio, streaming video, interactive
gaming, high-speed modems, etc., PCI provides a clear advantage
over older bus architectures.
PCI competes with both USB (see page 22) and IEEE 1394 (see
page 24) for high-bandwidth applications. All three provide the
advantage of Plug and Play installation, which may be important
to some users. Currently, only USB and IEEE 1394 support hot
swapping, but support for it is planned in a future PCI
specification. USB has been positioned as a low cost solution
for a variety of desktop applications. IEEE 1394 is used mainly
for video applications. However, PCI still has a speed advantage
when using true 64-bit data transfers. In fact, in many systems
USB or IEEE 1394 ports are added to a system via the PCI Bus
(see Quatech's TFC-100 page 69).
CompactPCI
PCI for Industrial Computers
CompactPCI is based on the electrical functionality of desktop
PCI and the Eurocard physical form factor. It is designed for
ruggedized applications in industrial environments. CompactPCI
boards have several features that make them ideal for embedded
systems or for industrial PCs:
• High density 2mm pin and socket connectors
• Designed for vertical card racks for better cooling
• Excellent vibration and shock protection characteristics
• Shield for EMI/RFI protection
• I/O connections on front or rear of module
• Staged power pins for hot swapping
Form Factor
The key to the CompactPCI bus is a gas-tight, high-density pin
and socket connector that meets the IEC-1076
international standard (pictured below).
Its low inductance and controlled impedance make it ideal for
PCI signaling. The connector uses a 2mm "Hard Metric" connector
and has 47 rows of 5 pins per row, with a total of 220 pins (15
pins are used for the keying area). An additional external metal
shield is also used. The large number of ground pins ensures
adequate shielding and grounding for low ground bounce and
reliable operation in noisy environments. By controlling
impedance, the connector can minimize signal reflections.
(CompactPCI 220 pin connector)
PCI and CompactPCI