Combinational logic vs sequential logic
So that it can work like a latch or flip-flop. If you still have doubt, let us know. We would explain it in a detailed way. In sequential circuit block diagram ,it is said that some outputs are again feedbacked to inputs,after storing them in memory. But,where is that memory in sr latch. In sr latch ,it is seen that the output is directly taken to the inputs,and their is no memory.
Memory in the block diagram shows a delay for which the previous output can be hold and can be used as the feedback input in the present clock cycle. So, there is no explicit memory block in the SR latch. Your email address will not be published. Notify me of follow-up comments by email. The logic gates which perform the operations on the data require a finite amount of time to respond to changes to their inputs.
This is called propagation delay. The interval between clock pulses must be long enough so that all the logic gates have time to respond to the changes and their outputs "settle" to stable logic values, before the next clock pulse occurs. As long as this condition is met ignoring certain other details the circuit is guaranteed to be stable and reliable. This determines the maximum operating speed of a synchronous circuit. Asynchronous sequential logic is not synchronized by a clock signal; the outputs of the circuit change directly in response to changes in inputs.
The advantage of asynchronous logic is that it can be faster than synchronous logic, because the circuit doesn't have to wait for a clock signal to process inputs. The speed of the device is potentially limited only by the propagation delays of the logic gates used. However, asynchronous logic is more difficult to design and is subject to problems not encountered in synchronous designs.
The main problem is that digital memory elements are sensitive to the order that their input signals arrive; if two signals arrive at a flip-flop or latch at almost the same time, which state the circuit goes into can depend on which signal gets to the gate first. Therefore, the circuit can go into the wrong state, depending on small differences in the propagation delays of the logic gates.
This is called a race condition. This problem is not as severe in synchronous circuits because the outputs of the memory elements only change at each clock pulse. The interval between clock signals is designed to be long enough to allow the outputs of the memory elements to "settle" so they are not changing when the next clock comes. Therefore, the only timing problems are due to "asynchronous inputs"; inputs to the circuit from other systems which are not synchronized to the clock signal.
In order for the channel selection to operate correctly, the television must be aware of which channel it is currently receiving, which was determined by past channel selections.
When a "channel up" or "channel down" input is given to it, the sequential logic of the channel selection circuitry calculates the new channel from the input and the current channel.
Digital sequential logic circuits are divided into synchronous and asynchronous types. In synchronous sequential circuits, the state of the device changes only at discrete times in response to a clock signal.
In asynchronous circuits the state of the device can change at any time in response to changing inputs.
Nearly all sequential logic today is clocked or synchronous logic. In a synchronous circuit, an electronic oscillator called a clock or clock generator generates a sequence of repetitive pulses called the clock signal which is distributed to all the memory elements in the circuit. The basic memory element in sequential logic is the flip-flop. The output of each flip-flop only changes when triggered by the clock pulse, so changes to the logic signals throughout the circuit all begin at the same time, at regular intervals, synchronized by the clock.
The output of all the storage elements flip-flops in the circuit at any given time, the binary data they contain, is called the state of the circuit. The state of a synchronous circuit only changes on clock pulses.
At each cycle, the next state is determined by the current state and the value of the input signals when the clock pulse occurs. The main advantage of synchronous logic is its simplicity. The logic gates which perform the operations on the data require a finite amount of time to respond to changes to their inputs.
This is called propagation delay.