Breaking News
Blog

First data's in the register, then it's not

Blog
11/10/2010 01:34 PM EST

 5 comments   post a comment
NO RATINGS
View Comments: Newest First | Oldest First | Threaded View
ReneCardenas
User Rank
Rookie
re: First data's in the register, then it's not
ReneCardenas   12/31/2010 6:08:01 AM
NO RATINGS
Even when specs define all supported configurations and features, you need to verify with prototyping early enough in your project. Unless you welcome surprises at the worst possible moment when the time pressure builds to a boil and no amount of money is able to justify a new tape out of Silicon. We had a case of complex telephony ASIC that was documented as supporting 8,16 or 32 bit wide flash memory. Unfortunately for us the smallest configuration was never tested by vendor!

Robert.Reavis
User Rank
Rookie
re: First data's in the register, then it's not
Robert.Reavis   11/13/2010 12:53:18 AM
NO RATINGS
Reminds me of testing a portion of the Space Station. One requirement for one of the boxes was to test the RS-422 signal for squareness with an oscilloscope. My lead engineer had it all setup through the switching matrix, but got ugly waveshape. Then, when manually debugging the test, the waveshape was perfect. Not knowing the history and not yet understanding the objective of the test, I asked why he had the scope probe tied to ground and also being switched to the other side of the RS-422 pair. The answer hit him like a lightning bolt. We cured the problem with a differential probe that measured the two data lines without pulling one of them to ground. Simple mistake, simple change, and a dramatic change in waveshape.

old account Frank Eory
User Rank
Rookie
re: First data's in the register, then it's not
old account Frank Eory   11/12/2010 9:15:30 PM
NO RATINGS
The lesson? Never leave inputs floating. I wonder how many designs...and designers...have been burned by this simple oversight.

sharps_eng
User Rank
Rookie
re: First data's in the register, then it's not
sharps_eng   11/11/2010 10:21:11 PM
NO RATINGS
Even reading the datsheet doesn't help sometimes. It was/is a little-known fact that the CD4538 monostable is different from the MC14538 monostable. That's right:- same chip, different vendors, standard logic family. One chip can retrigger before the pulse ends and the other can't; sometimes that REALLY matters! For all I know that is still the case with SM descendents and derivatives, depends on if RCA or Motorola were the design ancestor, e.g. NXP triggers like RCA, AFAIR. Never seen this quirk discussed or documented anywhere.

Rick_Hille
User Rank
CEO
re: First data's in the register, then it's not
Rick_Hille   11/10/2010 6:10:23 PM
NO RATINGS
To further underline your "thoroughly" assertion, one should also cover all of the fine print footnotes into which some vendors seem to take pleasure in hiding certain functional...er, let's just call them "distractions". Your story seminded me of a problem I ran into with an HDLC controller chip from the same era. In that case, however, even a close study of the datasheet and application notes (including the footnotes) would not have revealed the cause, although this does not diminish the valid point you make.

More Blogs
At Black Hat, researchers will point out the weaknesses in everything from the satellites in outer space to the thermostat in your home.
Meet Jibo, a connected personal assistant that aims to be your family’s first robot.
Neil and Buzz were on the moon. Orbiting above, there was Michael Collins. For a teenager, that summer posed no limits on the reach and social benefits of applied engineering and technology.
Matlab and Simulink are finding use in projects that don't necessarily require high-end math and signal processing.
Mobile devices will need a big boost in processing power to provide new features such as UltraHD video, LTE-Advanced, and 3D products (Google's Tango).
Most Recent Comments
Flash Poll
Radio
LATEST ARCHIVED BROADCAST
Join our online Radio Show on Friday 11th July starting at 2:00pm Eastern, when EETimes editor of all things fun and interesting, Max Maxfield, and embedded systems expert, Jack Ganssle, will debate as to just what is, and is not, and embedded system.
Like Us on Facebook

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
EE Times on Twitter
EE Times Twitter Feed
Top Comments of the Week