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Creating memory modules from smaller memory chips
To construct a 1Kxm module using m 1Kx1 chips, connect address and control pins in parallel.
To construct an nKxm module using 1Kxm chips, use logic gates or a decoder to generate a chip select signal.
Connect to the individual chip only those address lines that change when addressing specify locations on the chip.
Other address lines are used for chip select generation.
For a given microprocessor the number of bits per address is fixed. Sometimes we cannot find a memory chip that has the exact data width we need due to issues such as availability or cost. In such a situation, we can use several memory chips of narrower data width to construct a memory module of the width we need.
The basic idea is to determine how many chips are needed to provide the desired data width. The corresponding address pins and control pins of all memory chips are connected in parallel. Only the data pins of the memory chips are connected to the data bus separately.
The figure shown above is a schematic diagram that shows a 1KxM RAM module constructed from M 1Kx1 RAM chips.
Exercise: Draw a schematic diagram to make a 16Kx16 module using 16Kx4 chips.