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I have just started to learn how a microprocessor works and I have some questions.

I have read that the way the microprocessor read/writes data is by setting the address on the address bus, then setting high/low the read/write wire of the control bus and then to set the address bus valid control wire high to confirm the address we want to read. I read that this activate the memory chip select.

I didn't understand the 3rd part which says to set the address bus valid control wire high and what exactly the memory chip select purpose is.

Is there any chance that when we initially set the address and the read/write to high/low not to work thus we want the third step to set the address valid?

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When a microprocessor has external memory, like two RAM chips, the address bus and enable lines are decoded externally, so that the addresses you want for the first memory chip select it, and the addresses you want for the second chip select it. The exact order in which things happen may vary, and some buses have two enables, read and write, while some buses have single enable, with read/write selection.

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