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Semi-OT: LVDS and Cold Sparing

Hi,

Don't happen to have an LVDS specification (EIA-644) handy and couldn't find a freebie on the www. So hopefully someone out there has one.

Here's the question, I was told that section 4.4.2, & 6 have the fail-safe requirements. The issue is whether cold sparing capability is an LVDS requirement. I don't recall it being a requirement but I do want to go to the documentation to be sure.

My design does have cold sparing capability, it's the right thing to do for this particular application, so that is not an issue.

It is critical that the intent of the system designers, who state that they want cold sparing capability, be properly documented in the requirements (many users geographically and organizationally diverse) to avoid an oops. Having a specification buried in a third level referenced document that is not easy to obtain is a good opportunity for an oops.

But if cold sparing isn't part of the EIA-644 specification, then the top level specification that the systems guys are writing needs to be updated.

Thanks in advance,

--
rk, Just an OldEngineer
"These are highly complicated pieces of equipment almost as complicated as 
living organisms. In some cases, they've been designed by other computers.  We 
don't know exactly how they work."
-- Scientist in Michael Crichton's 1973 movie, Westworld
Reply to
rk
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What is "cold sparing"? I've never heard the term.

TC

Reply to
TC

If the device is powered off, the I/O's appear as high impedance. Then you can hook two devices together, one as a spare, and power off the one not being used at the time. In the application that I am considering, there are several sections of the system, not all of which are powered all the time, and I don't want to load down the source if I (sink) is powered off.

There's probably a more formal definition somewhere. But with typical CMOS I/O, you get a diode to the supply rail which can be problematic (also consider PCI systems with clamp diodes).

--
rk, Just an OldEngineer
"These are highly complicated pieces of equipment almost as complicated as 
living organisms. In some cases, they've been designed by other computers.  We 
don't know exactly how they work."
-- Scientist in Michael Crichton's 1973 movie, Westworld
Reply to
rk

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