Shift Registers:

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1 year ago

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Previously, we have seen the multivibrators, integrated circuits with the characteristic of changing from one state to another with the introduction of a single pulse (Clock) in one of its inputs (And depending only of this factor), falling these and much more I.Cs in the category of Combinational circuits. Now, we'll comment about some slightly different devices, the ones known as Shift Registers. First of all, these fall in the category of sequential circuits. What differentiates Sequential Circuits from Combinational Circuits is that the first not only depend in the signal introduced at the output, though also in the previous state that the circuit was, having the capacity to "remember". In the next paragraphs, we'll try to summarize what a shift register Is and what their configurations are.


What's a Shift Register?

A Shift register is an integrated circuit that is formed internally by the connection (in series) of many latches (which we explained previously in the multivibrators article) and other additional components, which will control the way we access or load information into the device. Their primary function is to delay or "shift" data to the next state (For example, the state of one bit in a certain sequence to the next bit in the right). In bigger circuits, they usually have the function of working as temporary storage for bits that are being processed in other operations.

Configurations of Shift Registers:

Shift Register can be divided according to two characteristic, their inputs/outputs relationship and the way the information is shifted. According to inputs and outputs, It can be categorized in 5 configurations:

  • Serial In/ Serial Out

  • Series In/Parallel Out

  • Parallel In/Serial Out

  • Parallel In/Parallel Out

  • Universal

Having into account that while operating, loading a byte (8 bits) into the device will be executed in different ways depending of the combinations. entering and going out in different ways.

Series In/ Serial Out:

In these, while loading the byte of information, the 8 bits composing It will pass through the input one by one and the time transcurring between the transference of each bit will be determined by the CLK Input, having that when transcurred 8 clock cycles, the bit will pass fully through the input of the device and they will process the information of the loaded byte the same way in the output.

Series In/ Parallel Out:

In this configuration, the byte is introduced through the input in the same way as the series input/series output, though now the output will show Itself in a parallel way (all bits of the byte at the same time).

Parallel In/ Serial Out:

Now the byte will be charged bit by bit in a parallel way, and the output will be presented in 8 clock cycles in series.

Parallel Input/ Parallel Output:

Data Is charged unto the device, all bits at the same time, and the resulting byte, will also come out bit by bit in the output.

Universal:

Meaning this that the shift register in this case can have any of the functionalities of the previously mentioned combinations, with the possibility to implement either parallel or series inputs and outputs.

Also, when regarding the way in which bits are shifted due to the shift register, we can divide them in two:

  • Unidirectional

  • Bidirectional

Meaning the first that the information shifts only in one direction, either left or right. With this we can easily find the concept and Its principal difference with the bidirectional type, which can choose to shift bits either to the left or to the right.


We hope that with the surface analysis of these beautiful devices that are often overlooked when designing circuits and their capabilities, you can find an useful tool for your projects and that It can serve you in your career. We always recommend working with the typical DC source voltage (5 v) in order to not damage the device.

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Your article reminded me of my last exam, where I had to go through a lot of videos to pass it. serial-in serial out , parallel etc. In fact everything. Good.

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