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Serial bus expands embedded computers flexibly

Jul 13, 2007 — by LinuxDevices Staff — from the LinuxDevices Archive — 2 views

Embedded board vendor VersaLogic has started shipping small, low-cost I/O boards based on a proprietary new expansion board format. The company's SPX (serial peripheral expansion) modules offer cost and space savings compared to traditional stacked PC/104 I/O boards, with no reduction in throughput or… capability, the vendor claims.

(Click for larger view of SPX I/O boards)

The small SPX boards measure 1.2 x 3.8 inches (30.5 mm x 96 mm). They connect to a host board, typically a single-board computer (SBC), via a proprietary SPI (serial peripheral interface) bus implementation said to require only a single small IC on either side the connection.

EBX SBC with a couple of SPX modules installed

The SPX modules can be physically bolted directly to host boards using PC/104 stand-offs, and electrically attached via ribbon cable. Mounting is simplified by virtue of a mounting hole spacing that matches those of PC/104 module stacks. The physical connector has 14 pins spaced at 2mm. Modules of the same or different type can be daisy-chained.

VersaLogic initially offers a six-inch cable supporting two modules, or a foot-long cable supporting four. The cables carry 500mA of 5.5-volt DC power to the modules, which can be located up to two feet from the host board. Modules typically use screw connectors for their I/O, VersaLogic said.

Len Crane, president, stated, “Invariably the on-board I/O features of a given SBC do not exactly meet the user's needs. The ability to economically add the last 5 or 10 percent will become more important as OEMs look to contain rising design and manufacturing costs.”

He added, “The SPX interface offers savings in terms of both cost and real estate, compared to traditional ISA-based devices, without a reduction in throughput or capability.”


Initially available SPX boards include:

  • 8-Channel analog input module
  • CANbus controller
  • 4-Channel analog output module
  • TTL I/O port expansion
  • 8-Channel solid state switch

Currently, the only VersaLogic SBC with an SPX expansion interface appears to be the Python VL-EBX-11, a Geode LX800-based EBX module announced in April. A second Python VL-EBX-22 board with SPX interface appears to be under development. And, the company plans to develop additional off-the-shelf SPX modules, it says, and to support companies requiring custom-designed SPX modules through its engineering group.

VersaLogic said its SPX modules and SPX-equipped boards are designed for extended temperature operation, RoHS compliance, and long-term availability. SPX modules are priced starting at $60 each, with volume discounts available. Quotes for custom modules are also available.

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