The control signals that select and read the data stored in ROM (Read Only Memory) or RAM (Random Access Memory) can appear complicated. A situation that can easily be remedied using computer graphics Here there are just four activities to consider. 1.) Select the address of the particular cell, this is achieved using a 2 - 4-line decoder. 2.) Do you want to Read or Write to that selected cell? Remember, for a ROM you can only read or NOT read it. Chip Enable you will have come across in other parts of this program. Chip Select or Chip Enable instructions allow the same address lines to be used for several devices. For this topic, CE is enabled by logic 0. The easiest way to become familiar with this topic is to input for each of the address, R/W and CE conditions and follow the logic through the various gates. Remembering that to activate an AND gate both inputs must be at logic 1. TEST YOUR UNDERSTANDING: If we make the memory address bus just one bit wider. What effect does that have on the amount of memory we can access?
