wire ORed

Thread Starter

swty_todd

Joined Aug 3, 2008
82
My textbook says that the output of comparators can be "wire ORed".
What does wire OReding an output mean?
 

Wendy

Joined Mar 24, 2008
21,840
It has to do with open collector outputs. If you tie a bunch of collectors together sharing one resistor it is equivalent to an OR gate. It was a common practice in the days TTL logic was king.
 

beenthere

Joined Apr 20, 2004
15,808
To expand a bit on Bill's post, those open collector outputs are all pulled up with a single resistor. Thus any one output can pull the common line low.
 

Thread Starter

swty_todd

Joined Aug 3, 2008
82
sorry i forgot to mention that the above sentence was in respect to uA311 precision comparator.
 

beenthere

Joined Apr 20, 2004
15,808
It has an open collector output - the second paragraph of the intro on the data sheet stated that the device can be wire OR'ed. Open collector outputs are open collector outputs.
 

leftyretro

Joined Nov 25, 2008
394
And of course wired OR can be accomplished by using series diode isolation between each of the 'voting' nodes and a single pull-up resistor so having open collector outputs is not the only way to be able to utilize wired OR stages.

Lefty
 
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