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Topic: understanding enable pin on some ICs (Read 756 times) previous topic - next topic

wilykat

on the datasheet if it shows pin has /ENABLE (line over the word but can't reproduce in text) does it mean the signal has to be low for the chip to work, and high for the chip to sit quietly, tristate all outputs, and do absolutely nothing?

aarg

The line means "inverted" or "active low".
  ... with a transistor and a large sum of money to spend ...
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terryking228

Quote
does it mean the signal has to be low for the chip to work, and high for the chip to sit quietly, tristate all outputs, and do absolutely nothing?
Excellent definition.  Elegant, even  :)
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aarg

Excellent definition.  Elegant, even  :)
But it might not be the case, as an enable signal may control part of the IC circuit, not all of it.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

wilykat

But it might not be the case, as an enable signal may control part of the IC circuit, not all of it.
True.  Many of the more complex 74xx, SRAM, EPROM, etc has single or 2 enable that controls the whole chip.  Some of the dual enable could be one keeps the chip active but tristates pin only and other puts the whole chip to inactive mode for lower power usage.  CBT3244 has 2 enable, one for each side (it is 4x SPST per enable, 2 sets per chip)

I just needed to be sure I got the nornal/inverted correct.  It'd suck if I discover after PCB fab that nothing works right because I got total of 16 enable done wrong, have to cut traces, wire in a bunch of inverters.

aarg

Don't trust the names. Go directly to the truth tables and/or timing diagrams.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

srnet

does it mean the signal has to be low for the chip to work, and high for the chip to sit quietly, tristate all outputs, and do absolutely nothing?
No, it depends on the chip itself, you need to refer to its data sheet for details.

You probably need to set the enable low to configure a chip or read from it, but with enable high it could well be active and working waiting for something external to the chip to happen and generate interrupt for instance.
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