Memory Structure and its Requirements

Memory Structure and its Requirements

As mentioned earlier, read/write memories consist of an array of registers, in which each register has unique address. The size of the memory is N × M as shown in Fig. 6.3.1 (a) where N is the number of registers and M is the word length, in number of bits.

Example 1  : If memory is having 12 address lines and 8 data lines, then

Number of registers/memory locations = 2^N = 2¹²

= 4096

Word length = M-bit

= 8-bit

Example 2  : If memory has 8192 memory locations, then it has 13 address lines.

The Table 6.3.1 summarizes the memory capacity and address lines required for memory interfacing.

As shown in the Fig. 6.3.1 (a) memory chip has 12 address lines A₀-A₁₁, one chip select  and two control lines, read  to enable output buffer and write  to enable the input buffer. The internal decoder is used to decode the address lines. Fig. 6.3.1(b) shows the logic diagram of a typical EPROM (Erasable Programmable Read-Only Memory) with 4096 (4 K) registers. It has 12 address lines A0-An, one chip select  one Read control signal. Since EPROM is a read only memory, it does not require the  signal.

Review Questions

1. Explain the memory structure and its requirements.

2. How much address lines are required to interface 4 kbytes of memory ?