# Advantage of multiple chip select lines

Let’s consider that the EPROMs we have are having the starting addresses as 4000H, 4400H, …, 5C00H. 4000H in binary is 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0. In such a case, the 74138 has to be selected for the condition A15 A14 A13 = 0 1 0. This can be achieved by the connection shown in below figure which uses two invert gates.

The procedure of selecting the chip74138 is denoted by the addresses A15 A14 A13 = 0 1 0 which can be implemented by any gates. We have taken the advantage of using multiple select pins of 74138 chip for the easy selection of chip process. Thus, wherever possible chip designers provide multiple chip select lines.

Fig. Simpler selection of 74138

Let us have EPROMs to get the address of starting like 4000H, 4400H, …, 5C00H respectively. In binary number 4000H is denoted as 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0. Here in that case, 74138 is selected for A15 A14 A13 to be 0 1 0 which we can get by the given connection as below -

Moreover, the selection of chip of 74138 for the condition A15 A14 A13 is 0 1 0. Only the advantage lies in the fact that that that it is easy mode of selection. We have taken the advantage of using multiple select pins of 74138 chip for the easy selection of chip process.

Fig. Selection of 74138 in simpler process.

Moreover, the selection procedure of the chip 74138 is given by the condition A15 A14 A13 = 0 1 0 done by help of any gates. Now the question arises why we have taken the help of multiple chips? It’s because just to make our work easy and simple. The procedure of selecting the chip74138 is denoted by the addresses A15 A14 A13 = 0 1 0 which can be implemented by any gates.