Page 115 - Digital Electronics by harish

Address in Binary data Data in
Binary D0 D1 D2 D3 D4 D5 D6 D7 Hex
00 1 0 1 0 0 1 0 1 A5
01 0 1 0 1 0 0 0 1 51
10 0 1 0 0 0 1 1 0 46
11 1 1 0 1 0 1 0 1 D5

Table : Data stored in ROM

4.9 Expanding memory

We need to expand the memory for the following two reasons.

1. To increase the word size (number of bits in each memory location).
2. To increase the memory capacity (number of locations).

4.9.1 Expanding word size

The word size i.e. the number of bits in the data lines can be expanded by connecting
two or more ICs together. The connection diagram is shown in figure.

Figure : Expanding word size of memory

The ICs are connected in such a way that the data lines are connected in series and the
address lines are connected in parallel. There are two 1K x 4 (1024 locations, each location
has 4 bits) memory ICs are used to get 1K x 8 memory. For 1024 locations, there are 10
address lines A0 to A9. Both memory ICs are selected simultaneously by common chip select
signal. When a particular address is given, both ICs are selected. Out of 8-bits, the first 4-bits
are taken from one IC and the next 4-bits are taken from another IC.

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