Monday, July 2, 2012

Analyzing SpaceWire Bus - Creating the Clock with Oscilloscope XOR

SpaceWire is one of the most exciting new technologies in the space electronics industry.  Previous designs used MIL-STD-1553, but are limited in speed to 1MB/s. SpaceWire (IEEE 1355.2) uses low-voltage differential signaling (LVDS) to push speeds from 2MB/s to 400MB/s.  For those who are in the commercial world, it may not sound incredibly fast, but it represents a huge improvement in the harsh environment of a spacecraft.  Today you can buy SpaceWire bus analyzers to see the detailed protocol, but as designs move from faster, many designers are discovering the need to look at the actual bits for signal integrity work.  Fielded designs are still using speeds below 100MB/s, but in the future it will likely be pushed to its limit.  In this first blog post, I will discuss how to generate the clock using the MATH system on your oscilloscope.  In future posts, I will discuss simple bit level decode and more advanced jitter and timing measurements.