Designing a small-form-factor system with interfaces like USB or SPI is relatively simple with a microcontroller and a custom board. But things get a little more interesting when you’re going between boards or starting with modules.
Module standards like COM Express (see “COM Express: A New Standard” at www.electronicdesign.com, ED Online 8780) and small board form factors like PC/104, MicroTCA, and VPX address midrange system design. Yet even smaller form factors are being used more often as the levels of integration continue to rise and chip size and power requirements fall. This is leading to the use of some older, compact standards as well as the emergence of some new ones.
The Compact Flash form factor has been quite common. Typically, it has been used for memory and a couple of peripheral interfaces such as Wi-Fi and Ethernet. C Data Solutions takes this form factor for its Compact Computer, or CoCo (Fig. 1).
The CoCo module contains up to a 750-MHz Analog Devices BG533 Blackfin digital signal controller, a Lattice FPGA, 16 Mbytes of flash memory, and 64 Mbytes of SDRAM. It has 50-pin connectors on each end.
The exposed I/O includes GPIO compatible with ITU-R 656 video, an SPI port, eight stereo I2S channels, a UART with IrDA support, and pulse-width modulation outputs. The FPGA is programmed as a Compact Flash UART, allowing the module to be plugged into a standard socket.
On another front, the Small Form Factor SIG announced its Stackable Unified Model Interconnect Technology (SUMIT) at the Embedded Systems Conference last month. SUMIT uses one or two Samtec connectors (Fig. 2) to link a singleboard computer to stackable adapter boards (see “Stacking PCI Express,” ED Online 8666) with a range of peripheral interfaces (see “SUMIT Connectors”).
Power is provided on both connectors with a large ground connection in the middle. Connector A, which can be used alone, includes common interfaces that are easy to implement. It also includes a single PCI Express link that can support an ExpressCard connection when it is combined with one of the USB connections.
This stacking interface comes with board specifications, putting it in the small-module category. It is an ideal complement to new platforms such as Intel’s Atom. Likewise, it will find a home where PC/104 currently lives. Using Connector A alone pushes it past PC/104-Plus.
PCI Express is clearly the new standard for peripheral interfacing, and SUMIT delivers support in a small package.
See associated table