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:
Answer
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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