These inputs, indicate binary values on output terminals by means of mixing with existing memory elements. Sequential circuits receive binary information via extrinsic inputs. The binary information stored within memory elements at a given period of time, explicates the state of a sequential circuit. Memory elements are devices which have a capacity to store binary information within it. A sequential circuit comprises a feedback path between combinational circuit and memory elements, as has been represented by a block diagram of the sequential circuit in figure 5.1. flip-flop is a basic chip which is being used on a sequential circuit. In other words, basic feature of a sequential circuit has been memory or sequential circuits are a type of circuits, which have a capacity to store binary numbers. these circuits are manufactured through the assistance of different logic gates), whereas sequential logic circuits are used in timing and memory devices and flip-flop serve as a building block on them. In combinational logic circuits (about which we have already read in the previous chapters) gates serve as basic building block (i.e. The following types expounds the difference between operations of these two types of logic circuits. Logic circuit is normally divided into two types. Flip-flops are mostly used in the construction of registers, counters and timers etc. Flip-flop is a basic memory element and it is also known as a bistable multi – vibrator. It is a prominent feature of a flip-flop that as long as status of its input signal is not changed, it remains indefinitely on any one of the afore – mentioned two states (as long as power is transmitted on the circuit). In other words, a digital element, which can store only one bit of a binary data, is known as a flip-flop. Only the changes of state will be synchronized by a clock “clk” (clock = clock in English).Flip-Flop Combinational logic circuits and Sequential logic circuits- Flip-flop is a memory element, which can store at a time either binary 1 or binary 0. The operation is the same as that of an elementary RS flip-flop. We therefore prefer to prohibit the combination R = S = 1! So when we go from the state R = S = 1 to R = S = 0, one of the inputs A or B will go to 1 before the other, which will make either Q or / Q go to 0 But we cannot know which of A or B will be at 1 before the other, so we cannot precisely determine the state of the output … We say that there is an indeterminacy on the output. Indeed, even if they come from the same manufacturer, their switching times will always be slightly different. So when we want to go from the state R = S = 1 => Q = / Q = 1 to l ‘state R = S = 0 => Qn + 1 = Qn then the outputs should remain unchanged (= 1).īut in practice it is necessary to consider the switching times of the logical operators. if R = S = 1: we therefore have A = D = 0 => Q = / Q = 1.We say that the RS flip-flop is in “memory” state. We therefore notice that when R = S = 0, the state of the outputs is unchanged: if R = S = 0 at an instant “n + 1” then the Q and / Q outputs will keep the state they had at l ‘previous instant “n” => Qn + 1 = Qn (and / Qn + 1 = / Q obviously). In fact at an instant “n + 1”, the state of the NANDs will depend on the state of Q and of / Q at the previous instant “n” (this is the principle of sequential logic!). if R = S = 0: we therefore have A = D = 1, so we cannot comment on the state of the NANDs.Let us now analyze the states where R and S are identical: Or / Q = B = 1, moreover like S = 0 => A = 1 => Q = 0. if R = 1 and S = 0: R = 1 => D = 0 => / Q = 1 whatever C.if R = 0 and S = 1: S = 1 => A = 0 => Q = 1 whatever B.Let’s start by analyzing the states where R and S are different:
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