Back in February, I wrote about the emergence of a new consortium, the Small Form Factor (SFF) Special Interest Group (SIG). At the time, I questioned whether there was really a need for not just a new consortium, bit a new board form factor for designers to adhere to.
While I'm still not completely sold on the idea, I understand the justification. There's actually more of a need for the new form factor than there is for the SIG. The form factor, called Express104, is a module that incorporates Stackable Unified Module Interconnect Technology (SUMIT) expansion. It supports an embedded processor plus one or more stackable I/O modules in a small space.
SUMIT defines two high-speed connectors and their respective signal assignments; however, it doesn't address the specific placement requirements for the connectors. Only the relative location of one connector to the other is specified to ensure proper signal routing in a stacked architecture.
Express104 is defined as a stackable 90- by 96-mm board with two 52-pin, high-speed connectors that can support PCI Express and USB data rates, as well as other I/O interfaces, while preserving signal integrity. The rugged capability allows it to fit a a wide variety of applications.
One of the nice features of Express104 is its backward compatibility with PC/104. Hence, designers can plug in either Express104 or PC/104 modules, thereby maintaining legacy support for the existing base of PC/104 expansion I/O modules and enclosures already available. Also, Express104 is an open standard, meaning that no licensing fees are required for implementation. But if you want to use the SFF SIG logos, you must join the SIG.
The jury is still out on whether this new standard will become a mainstay. We'll know more as real products become available. Maybe I'll wait till them to pass judgment (again).
Richard Nass is editor in chief of Embedded Systems Design magazine. He can be reached at .