ABSTRACT
To achieve a given output, it is often necessary to use combinations of switches connected both in series and in parallel. If the output from a switching circuit is given by the Boolean expression: Z A . B A . B , the truth table is as shown in Figure 10.5(a) . In this table, columns 1 and 2 give all the possible combinations of A and B. Column 3 corresponds to A . B and column 4 to A . B i.e. a 1 output is obtained when A 0 and when B 0. Column 5 is the or-function applied to columns 3 and 4 giving an output of Z A . B A . B . The corresponding switching circuit is shown in Figure 10.5(b) in which A and B are connected in series to give A . B, A and B are connected in series to give A . B , and A . B and A . B are connected in parallel to give A . B A . B . The circuit symbols used are such that A means the switch is on when A is 1, A means the switch is on when A is 0, and so on.
