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Mezzanine Modules
When you run out of room in an embedded system, you can always move up to the mezzanine level. That statement isn't as facetious as it sounds. Many single-board computers and cards for VMEbus, cPCI, and other buses provide for add-on mezzanine modules. Because these modules connect directly to an existing board and mount within that board's volume, they consume neither an additional bus slot nor an extra card space.
Why not just start with a processor board that offers the I/O and communication devices you need and dispense with mezzanine modules? Customers' wide-ranging demands for Ethernet, USB, FireWire, RS-232, Fibre-Channel and other communication ports - and for analog and digital I/O - make it impossible to answer every need with a few types of CPU boards. Thus, the add-a-module approach lets buyers customize a general-purpose CPU board that furnishes mezzanine-module connectors. The designers can choose the proper mix of communication and I/O connections for a task.
The use of mezzanine modules also simplifies hardware upgrades. Should I/O needs change, the underlying equipment can remain in place while system developers change the mix of mezzanine modules to address new electronic requirements. In addition, as CPU-board designs advance, developers can upgrade the processor board while they continue to use the same mezzanine modules for communications, graphies, I/O and other purposes. Several mezzanine-module standards, such as PMC and PC-MIP, let system developers choose the processor card, module-carrier boards and modules a system requires (Figure 1).
PCI Holds the Cards
The PCI Mezzanine Card (PMC) takes advantage of the popular Peripheral Component Interconnect (PCI) bus found in most personal computers. Because the PC industry broadly supports the PCI bus,...