25-02-2013, 11:46 AM
8 to 1 line MULTIPLEXER
MULTIPLEXER.doc (Size: 277 KB / Downloads: 24)
INTRODUCTION
(Many into One) The function performed by a multiplexer is to select 1 out of N input data sources and to transmit the selected data to a single information channel. An electronic multiplexer makes it possible for several signals to share one device or resource, for example one A/D converter or one communication line, instead of having one device per input signal.It is a combinational circuit & is used in designing digital circuits.
The logic system for a N to 1 line data selector- multiplexer is as shown. There will be m select signals such that N≤ 2m .By selecting proper select code one of the line will be connected to the output line. A enable or strobe input signal is also used to cascade different multiplexers ,which is normally low.
WORKING
Only one of the 4 bits D0 to D3 is transmitted to the output. Which one depends on the value of S1 & S0, the control inputs. If S1S0=00 the 1st AND gate is enabled while all other AND gates are disabled. \ data bit D0 is transmitted to the output, thus Y=D0.If the control signal is 10 , all the gates are disabled except 2nd AND gate, thus Y = D1 & so on.Thus control signal determines which of the input data bit is to be transmitted to the output.
MULTIPLEXER LOGIC
Any given truth table can be implemented using multiplexer, the method is called multiplexer solution.
Advantages: 1)Simplification 2) It minimizes the IC package counts. 3)Logic design is simplified.
Method 1: used is SOP: 1)Locate ‘1’ in the truth table corresponding to each minterm ,& identify the decimal number.The input Line corresponding to these numbers are connected to Vcc.
2)All other lines are connected to logic 0 i.e. GND.
3)Now inputs are applied as select signals.
For example consider the truth table for the expression