DATASHEET OF IC 74154 PDF

Arashinos It is counterintuitive yes, but it is a well-established convention that the sort of devices that this part will be controlling will have active-low enable inputs. I understand how it works. It is active low output IC so when any output line is selected it is indicated by active low signal, rest of the output lines will remain active high. For the proper working of this local control section except the local telephone set it needs a permanent back up which gives a 5V back up continuously.

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Akigul The active-low enable inputs allow cascading of demultiplexers over many bits. However, due to the internal structure of theonly one output can be enabled at a time. Sign up using Facebook. If you wanted to generate a 1 of demultiplexer, you could use 16 s looking at the 4 least significant bits, while a single would look at the 4 most significant bits, with one ouput going to each of the other 16 s. Why is the output in the truth table inverted in a ic used as a demux?

Why are the outputs inverted? I understand how it works. National Semiconductor It is counterintuitive yes, but it is a well-established convention that the sort of devices that this part will be controlling will have active-low enable inputs. The active-low output is just how the design for that specific decoder was carried out — there is also active-high varieties.

High speed signals were usually active low, for much the same reason. The demultiplexing function is performed by using the 4 input lines to address the output line, passing data from one of the strobe inputs with the other strobe input low. Sign up or log in Sign up using Google. I have a doubt in the demultiplexer section. This all has to do with the actual ic design. Rather than providing only a single enable, both pins are used.

PDF Datasheet download Inputs were pulled high by default, and only pulled low when necessary, to save power. This chip is often used in demultiplexing applications, such as digital clocks, LED matrices, and other graphical outputs. Each of the 16 outputs can be connected through a resistor and then through an LED to serve as a simple 16 LED controller. Home Questions Tags Users Unanswered. According to the internal logic diagram on the datasheet, the G inputs are connected to a two-input AND gate with inverting inputs, whose output feeds one input of all the NAND gates that produce the outputs.

But when we try to implement a demultiplexer using a TTLthis is the truth table that is given in the book: If you want to know exactly what is going on then draw out the truth table, but it is unlikely their function will make much sense to you. Is the hardware implementation circuit different than the one explained in theory?

So you can use a 47 kilohm resistor to pull up drops 1. For example, if the target application requires 16 7-segment LED displays, but your microcontroller only has 4 lines to select which display is active, this chip 74LS would provide a very effective method of essentially multiplying you selecting lines by a 4 times. All inputs are buffered and input clamping diodes are provided to minimize transmission-line effects and thereby simplify system design.

Each or these 4-line-toline decoders utilizes TTL circuitry to decode four binary-coded inputs into one of sixteen mutually exclusive outputs when both the strobe inputs, G1 and G2, are low. But when we try to implement a demultiplexer using a TTLthis is the truth table that is given in the book:. Post as a guest Name.

Email Required, but never shown. The person who took time to answer the question will appreciate that. This allows more flexibility in the logic functions available. Will someone please explain the purpose of inverting the outputs 0 through 15 as well as the use the NAND gates here?

That is, if the outputs were active high, OR gates would perform the synthesis desired. Sign up using Email dagasheet Password. National Semiconductor — datasheet pdf Post as a guest Name. The actual implementation of the chosen ic has active low outputs.

Many TTL parts and older memory chips have active low enable inputs, so the active low outputs of this part can be connected directly to those inputs. So theory will cover only the theory which explains the basic functionality of the working of a demultiplexor.

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And this carried through to the way the logic was used, and designed with. Related Posts

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DATASHEET OF IC 74154 PDF

You can upvote more than one answer. Since the ouputs are active low, NAND gates do the job. Sign up using Email and Password. According to the internal logic diagram on the datasheet, the G inputs are connected to a two-input AND gate with inverting inputs, whose output feeds one input of all the NAND gates that produce the outputs. By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. Inputs were pulled high by default, and only pulled low when necessary, to save power. The active-low enable inputs allow cascading of demultiplexers over many bits.

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National Semiconductor

Brashakar By using this project we can construct the personally branched telephone exchange. For producing the appropriate signals it is necessary that a crystal oscillator of dahasheet. After a period of 5 seconds the output of the IC 6 goes low and puts the tri state buffer in the high impedance state. These flip-flops are used to latch the data that present at its input terminal click here to download datasheet.

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The demultiplexing function is performed by using the 4 input lines to address the output line, passing data from one of the strobe inputs with the other strobe input low. Sign up using Email and Password. This carried through to the input current requirements: Sign up using Facebook. Is the hardware implementation circuit different than the one explained in theory? This all has to do with the actual ic design. Inputs datasheet pulled high by default, and only pulled low when necessary, to save power. Why is the output in the truth table inverted in a ic used as a demux?

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