4-line to line Decoders/demultiplexers. Each or these 4-line-toline decoders utilizes TTL circuitry to decode four binary-coded inputs into one of. MOS technology. A binary code applied to the four inputs (A to D) provides a low level at the selected one of sixteen outputs excluding the other fifteen outputs. SNN .. of significant portions of TI information in TI data books or data sheets is permissible only if reproduction is without alteration.
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Datasheet pdf – 4-Line to Line Decoders/Demultiplexers – National Semiconductor
First, the inversion of the outputs simply means that the output is active low. That is, for an input ofthe 0 output is selected, and it is driven low. All the other ouputs stay high. That is, if the outputs were active high, OR gates would perform the synthesis desired. Since the ouputs are active low, NAND gates do the job.
The active-low enable inputs allow cascading of demultiplexers over many bits. 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 datasheft.
Datasheet(PDF) – National Semiconductor (TI)
And why are there 2 of them, you datasehet Rather than providing only a single enable, both pins are used. This allows more flexibility in the logic functions available. 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. There are probably two enable inputs because otherwise there would be two unused pins on the 24 pin package I don’t recall seeing 22 pin DIP packages.
The active-low output is just how the design for that specific decoder was carried dayasheet – there is also active-high varieties. As for the NAND gates, there is a function being implemented in which the gates are there to realize it.
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.
My first question is more important WhatRoughBeast 49k 2 28 Please consider upvoting those questions you found useful like this one by clicking the arrow pointing up near the answer vote count which is in turn above the checkbox you clicked to accept this question.
The person who took time to answer the question will appreciate that. You can upvote more than one answer. I am a new user so I didn’t know I had that power. So is it possible that both enables 74145 hooked to a 2-input OR gate; this is just making use of the extra pins to make 24?
74154 Datasheet PDF
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 7454 all the NAND gates that produce the outputs. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.