Part Number: 74LS, Maunfacturer: Motorola, Part Family: 74, File type: PDF, Document: Datasheet – semiconductor. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may. r/Demultip lex e r. 74LS / 74LSSMD / 74LS Decoder/Demultiplexer. General Description. These Schottky-clamped circuits are designed to be used.

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Forms maths Geometry Physics 1. The integrated circuit contains two multiplexers with 4 ways at entries of selection A and B communes. This one, carried to the state 1force the exit of the multiplexer corresponding to state 0 independently of the state of the other datsheet.

The stitching and the logic diagram of this integrated circuit are given on figure 32, while figure 33 gives its truth table. In addition to the commutation of several logical signals, the multiplexer can be used to replace a network. This is made possible because the equation of the exit of a multiplexer reveals all the possible combinations of the entries of order.

The exit S with for the equation: Since all the combinations of the entries A, B, C and D are present in this equation, we can fulfill with this multiplexer any switching function comprising the same number of entries, that is to say 4. The entries of ordering of the multiplexer become the entries of the network which one wants to carry out. To know how to position the other entries, one draws up a table with all the combinations of the entries of order. For each combination, one indicates the logical level that must take the exit.

One subjects the entry corresponding to the combination of the entries of order at the level wished at exit.

The example which follows will clarify the procedure. One has four switches being able to be datasueet either to the supply voltage, or with the mass and one wants to know so at least two switches are closed again on the positive tension of food. A circuit of this kind can be used for the indication of breakdowns, or for 7413 counting of parts 774139 a production line.


If integrated logical doors are used, one obtains the circuit represented on figure The exit of the circuit is brought to the level H when at least two of the reversers are commutated on the positive tension. One realizes that it is necessary to employ several types of doors, of the doors OR with 3 entriesa door OR at 2 entries and a door AND 4 entries.

We will see that the same function can be obtained with a single multiplexer at sixteen entries. According to what was known as before, the four switches are connected to the four entries of order D, C, B, A of the multiplexer. To determine how to connect the sixteen inputs, it is enough to follow the described procedure and to build a table with sixteen lines like that of figure For each combination of the entries of order, one defers in the column of the exit the state that this one must take.

In the table of figure 35, the lines represented in red characters correspond if at least two of the entries of order are on the level H and for which the exit must thus be with the level H. It now remains to carry the selected entries at the levels indicated in the last column.

74139 Datasheet PDF

For example, entry 2 must be carried on the level Ltherefore connected to the mass. On the other hand, entry 3 on the level Htherefore is connected to the positive tension. The circuit which results from it is deferred on figure The advantage of the multiplexer compared to the network of doors is obvious: This one indeed requires at least three integrated circuits: Moreover, the use of a multiplexer makes it possible to pass easily from a switching function to another by changing the level of the inputs.

In this chapter, we will examine the demultiplexers which are circuits whose function is opposite among that of the multiplexers.

Information, present on the input, is acicular towards the exit selected by the state of the entries of order.

The not selected exits position with state 1. Let us examine simplest of the demultiplexers, that with 2 ways. The diagram symbolic system and the mechanical equivalent of a demultiplexer with 2 dtaasheet are presented at figure The data present in D is acicular towards S0 or S1 depending on the 744139 of the entry of order A.


The combinative circuit which fulfills the function of the demultiplexer with 2 ways must thus correspond to the truth table of figure To find the equation simplest of S1let us draw the picture datasheeet Karnaugh figure The two groupings and D give us the following equation of S1: The expressions and lead us to the logic diagram of figure One does not find a demultiplexer with 2 ways integrated.

If one has the integrated circuitone can carry out the circuit of figure Otherwise, it is necessary to turn to the demultiplexer integrated into 4 ways: The integrated circuit 74LS contains two demultiplexers with 4 ways. The stitching and the logic diagram of this circuit are given on figure 41, while figure 42 gives its truth table. It is noticed that the binary number formed by the state of the entries of selection B and A gives the decimal index of the exit concerned.

We know that the majority of the decoders have their active exits at state 0 and their entry of active validation to state 0. Let us carry the entry of validation to state 0: Now let us carry the entry of validation to state 1: In short, the logical data present on the entry of validation is acicular towards the exit selected by the entries of the decoder.

Thus to use a decoder out of demultiplexer, the entry of validation becomes the input and the datasheett of the decoder become the entries of ordering of the demultiplexer. Figure 43 illustrates how one passes from a decoder to a demultiplexer.

The next theory will treat memories. Click here for the following lesson or in the synopsis envisaged to this end.

(Datasheet) pdf – Dual 2 to 4 Demultiplexers (1-page)

High of page Preceding page Following page. Use of a decoder out of demultiplexer. Return to the synopsis. To contact the author. Static page of welcome. Dynamic page of welcome.

74LS Datasheet(PDF) – TI store

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