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I have a pretty good concept of Encoders and Decoders, but I can't get insight on the "Active High" keyword, and there are two enable lines which confuses me. I encountered the problem while working with a microprocessor address decoding circuit. I have an image here:

enter image description here

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    \$\begingroup\$ The symbol is incorrect. The "bubbles" on the outputs generally indicate active-low. "Active-High" (or "active-low) in the context of describing a decoder generally refers to the outputs. \$\endgroup\$
    – Tut
    Dec 5, 2017 at 12:50

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Some devices do indeed have multiple enables, some have a mix of high and low. This is partly done to make the device more convenient for use and, in some cases I am fairly sure, were added to use up all the pins on the package.

It is common to use them to divide up the functionality when using them for address decoding.

Looking at your circuit above, you could double up that circuit to have a read decode and a write decode. In which case one would have the /E line attached to whatever /Write_Enable line comes from the micro, while the other would have the active high E pin connected to /Write Enable.

For a decoder, you can also use them as additional address lines, or to clock, synchronize, the output.

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Active high tells you the polarity of a digital signal. It means that the digital signal is asserted, is active, causes its thing to happen, when high.

Note that the bars over the names of the E1 and E2 inputs means they are active low.

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  • \$\begingroup\$ @Sur: Of course, by reading the datasheet. \$\endgroup\$ Dec 5, 2017 at 12:06

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