A serial Boolean logic unit has two 16-bit shift registers,A and B.A control signal (C) is used to select the Boolean operation to be performed .
If C = o, the contents of A are serially replaced by the bit-by-bit Boolean AND of A and B. If C = 1, the contents of A are serially replaced by the bit-by-bit exclusive-OR of A and B. After the numbers have been placed in A and B, and C is set to o or 1, a start signal (St) sets the circuit in operation. A counter is used to count the number of shifts. When the counter reaches state 15, it outputs a signal K = 1, which causes the control circuit to stop after one more shift. Assume that St remains 1and C does not change until the operation is completed.The control then remains in the stop state until St is changed back to o.
(a) Draw a block diagram of the system,which includes the shift registers, the counter, the control circuit, and a logic circuit that generates the serial input (SI) to theA register.
(b) Draw a state graph for the control circuit (three states).
(c) Design the control circuit using a PLA and D flip-flops.
(d) Design a logic circuit that generates SI.