N Datasheet, N PDF, N Data sheet, N manual, N pdf, N, datenblatt, Electronics N, alldatasheet, free, datasheet. Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise . 3. Ordering information. 74HC; 74HCT 4-to line decoder/ demultiplexer. Rev. 7 — 29 February Product data sheet. Table 1. Ordering .
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N Datasheet, PDF – Alldatasheet
First, the inversion of the outputs simply means that datasgeet 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.
Circuits Intégrés Logiques TTL
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 s. And why are there 2 of them, you ask?
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 datashet part can be connected directly to those dwtasheet.
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 out – there is also active-high varieties. As for the NAND gates, there is a 74154nn 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.
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So is it possible that both enables are hooked to a 2-input OR gate; this is just making use of the extra pins to make 24? 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.