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cerebrum
PostPosted: Thu Feb 07, 2013 2:32 am 
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Joined: Mon Jan 28, 2013 3:09 am
Posts: 35
According to the dictionary a latch is:

Quote:
Also called latch circuit Electronics a logic circuit that transfers the input states to the output states when signalled, the output thereafter remaining insensitive to changes in input status until signalled again


As an example see:
https://en.wikipedia.org/wiki/Transparent_latch#Simple_set-reset_latches

What is the connection to the mechanical latch(aka lock)? Is it that the output is locked until the correct signal will set it to a new value?
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Dr Jefyll
PostPosted: Thu Feb 07, 2013 5:15 am 
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Hi cerebrum.

I can't speak with the authority of a dictionary, but I will share with you my own mental picture of why the word "latch" is appropriate. I think of a door that might swing one way or the other at any time. That could be inconvenient. If so, you might wish to temporarily latch the door to stop it from changing position. Hope that helps,

Jeff

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BigDumbDinosaur
PostPosted: Thu Feb 07, 2013 7:09 pm 
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Perhaps the image of what a deadbolt does might help. It can be latched, i.e., placed into the locked position, thus preventing the door from opening (changing state, as it were). When the deadbolt is unlatched, the door may be opened (can change state). The term is actually quite apt for the function that it describes.

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bogax
PostPosted: Fri Feb 08, 2013 7:31 am 
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They used to (and still do) impliment them with
actual latches on relays.
How that might relate I don't know, but I'd guess
there some lineage of etymology there.
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BigDumbDinosaur
PostPosted: Sun Feb 10, 2013 6:13 am 
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bogax wrote:
They used to (and still do) impliment them with actual latches on relays. How that might relate I don't know, but I'd guess there some lineage of etymology there.

The trick of a relay latching itself dates back to the 19th century, and has found application in wide variety of devices (I'm most familiar with latching relays in telecommunications switching systems). There are several methods of getting a relay to latch:

  • Using one of its contacts to maintain coil power, will not maintain state without power;

  • Mechanical latching using dual armatures and coils, will maintain state without power;

  • Remanent magnetism with a single or dual coils (one to latch and one to release the relay), which doesn't rely on a mechanical latch but maintains state with or without power.

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