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## 8.10 Analysis of Synchronous Sequential Circuits

As mentioned earlier, a sequential circuit contains one or more flip flops and may or may not include logic gates. The circuits in Figure 8.20 are both sequential circuits.

Figure 8.20: Examples of sequential circuits

The circuits of Figures 8.20(a) and 8.20(b) are both clocked by the clock pulse CP. The circuit of Figure 8.20(a) is also synchronous since the clock pulse CP is applied simultaneously at all three JK flip flops.

The analysis of synchronous sequential logic circuits is facilitated by the use of state tables which consist of three vertical sections labeled present state, flip flop inputs, and next state. The present state represents the state of each flip flop before the occurrence of a clock pulse. The flip flop inputs section lists the logic levels (zeros or ones) at the flip flop inputs which are determined from the given sequential circuit. The next state section lists the states of the flip flop outputs after the clock pulse occurrence. The procedure is illustrated with the following examples.

Example 8.2

Describe the operation of the sequential circuit of Figure 8.21.

Solution:

First, we observe that the JK flip flops are enabled at the negative edge of the clock pulse. Also, the Set Direct S D and Reset Direct R D signals are asynchronous active Low inputs, that is, when they are Low, they override the clock and the data inputs forcing the outputs Q to a...

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Flip-Flops
Flip-flops are digital logic devices that synchronize changes in output state (1 or 0) according to a clocked input.
Logic Counters
Logic counters are integrated circuits used for counting events in computers and other digital systems.
Shift Registers
Shift registers are sequential logic circuits that are used to store and move data. They accept binary inputs from one serial or parallel source and then shift the data through a chain of flip-flops, one bit at time.
Field-Programmable Gate Arrays (FPGA)
Field-programmable gate arrays (FPGAs) have a different architecture than SPLDs and CPLDs, and typically offer higher capacities. FPGAs are also known as logic cell arrays (LCA) and programmable ASIC (pASIC).
Logic Latches
Logic latches are logic devices that latch onto or retain digital states (1 or 0) in data storage circuits.

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5.5 Sequential Logic Design 5.5.1 Introduction Sequential logic circuits are based on combinational logic circuit elements (AND, OR, etc.) working alongside sequential circuit elements (latches...

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