Multiplexer
Multiplexing means transmitting a largo number of information units over a smaller number of channels or lines. A digital multiplexer is a combinational circuit that selects binary information from one of many input line and directs it to the output line. The selection of a particular input line is controlled by a set of selection line, Normally, there are 2n lines and n selection lines whose bit combinations determine which input is selected.
The Selection of inputs will be as of the above Table
When Si = 0 and So = 0. Output of gate 2, 3 and 4 will be 0, and the output of gate 1 will depend upon /0 (because So =1 and Si = 1, thus output of gate 1= /o • 1.1= /0)
S1 S1 so So
Combinational circuit for 4 x 1 multiplexer
Demultiplexer
A demultiPlexer is a circuit that receives information on a single line and transmit that information on one of 2n possible output lines. The output line to which input will be transmitted is selected by the selection line.
Sequential Circuit
A switching circuit whose output depends not only on the present state of its input but also what its input conditions have been in the past.
Sequential logic output depends on stored levels and also the input
levels. The memory elements are capable of storing binary information.
A sequential circuit is specified by a time, sequence of inputs, output and internal states.
Key Points
- There are two types of sequential circuits. This classification depends on the timing of their signals.
- Asynchronous sequential circuits
- Synchronous sequential circuits
Asynchronous Sequential Circuits
This is a system whose outputs depend upon the order in which its input variable change and can be affected at any instant of time.
Synchronous Sequential Circuits
These circuits have a clock signal as one of their inputs to force the change in output only at discrete instance of time. As state transition in such circuits occurs
only when the clock value is either 0 or 1 or happen at rising or falling edge of the
clock.
The memory element used in the synchronous sequential circuits is called flip-flops.