memory devices designed to connect to a bus (such as RAM and ROM chips) have both and (output enable) pins, which superficially appear to do the same thing. If is not asserted, the outputs are Hi-Z.

The difference lies in the time needed to output the signal. When chip select is deasserted, the chip does not operate internally, and there will be a significant delay between providing an address and receiving the data. (An advantage of course, is that the chip consumes minimal power in this case.)

When chip select is asserted,

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