A PCI Mezzanine Card or Media Center Switched Mezzanine card (XMC) is a printed
circuit board assembly manufactured to the IEEE P1386.1 standard. This standard combines the electrical characteristics of the PCI bus
with the mechanical dimensions of the Common Mezzanine Card or CMC format (IEEE 1386 standard).
A mezzanine connector connects two parallel
printed circuit boards in a stacking configuration. Many mezzanine connector
styles are commercially available for this purpose, however PMC mezzanine
applications usually use the 1.0 mm pitch 64 pin connector described in IEEE
1386.
A XMC/PMC can have up to four 64-pin bus connectors. The first two ("P1" and
"P2") are used for 32 bit PCI signals, a third ("P3") is needed for 64 bit PCI
signals. An additional bus connector ("P4") can be used for non-specified I/O
signals. In addition, arbitrary connectors can be supplied on the front panel of
the chassis or case; also known as a "bezel".
The PMC standard defines which connector pins are used for which PCI signals; in
addition it defines the optional 64 "P4" connector pins for use of arbitrary I/O
signals.It enables manufacturers to offer products that are compatible with the
well-established PCI bus, but in a smaller and more robust package than standard
PCI plug-in cards.
The word mezzanine, derived from the Italian mezzanino and also commonly used to refer to a platform
inserted between two floors of a building, describes the way in which a PMC fits
between two adjacent host cards in a standard card rack, attached to one of the
cards by connectors and mounting pillars. A single PMC measures 74 mmx149 mm.
The standard also defines a double-sized card, but this is rarely used.
Carrier cards that accept PMCs are usually made in the Eurocard format, which includes single, double and triple-height VMEbus cards, CompactPCI(cPCI)cards and more recently,VPX cards.
One PMC fits on a standard 3U carrier
card while 6U models (typical for VMEbus cards) can carry up to two PMCs. PMCs were also used in early ATCA systems prior to the
advent of the Advanced Mezzanine Card or AMC. For the PMC standard, I/O technologies account for much of the market, but
various card functions are commercially available including Intel architecture
and PowerPC processors, graphics cards, and memory cards. I/O cards are
available such as serial communication controllers, SCSI controllers, graphics controllers and FireWire controllers.
