Shift Registers in LabVIEW

When programming with loops in LabVIEW, you often need to access data from previous iterations. This is where shift registers come in. Shift registers are pivotal in handling dynamic data across LabVIEW iterations. 

Implementing shift registers can help you develop high-performance LabVIEW applications. This article provides examples to help you understand shift registers' capabilities and implementation.

Let’s dive in!

Table of Contents

• Introduction to Shift Registers in LabVIEW
• How do you create a shift register in LabVIEW?
• Initialising a Shift Register
• Using a shift register in a while loop – Example
• Stacked Shift Registers
• Replacing Shift Registers with Tunnels
• Feedback Nodes
• Common use cases of shift registers in LabVIEW
• Best practices in using shift registers in LabVIEW
• Summary
• FAQs

Introduction to Shift Registers in LabVIEW

Let’s start with the fundamentals of shift registers in connection to the LabVIEW software.

• Shift registers are powerful manipulation tools used in LabVIEW. 
• They are memory elements with two terminals attached to the loop’s boundary. 
• They allow data to be passed between loop iterations.
• They are similar to local variables used inside loops in text-based languages.
• The left panel holds the input value, and the right panel has the output value that will be passed to the next iteration.

How do you create a shift register in LabVIEW?

Let's learn how to create a shift register in LabVIEW.

Shift registers can be used with ‘For’ and ‘While’ Loops to transfer values from one loop iteration to the next. 

Below is the step-by-step procedure for creating a shift register in LabVIEW.

Step 1: Open a VI in LabVIEW.

Step 2: Placing a while loop

• Go to the block diagram
• Click the view tab and select the functions palette.
• Click structures in the functions palette and drag a while loop into the block diagram, as shown in the image below.

Step 3: Adding Shift Registers

• Right-click on the borders of the while loop
• Select ‘add shift register’ from the menu

• A shift register will appear as a pair of terminals opposite each other on the vertical sides of the loop border.
• Now, you will see two shift registers on the left and right side of the while loop.
• The terminal on the right side of the loop contains an up arrow and stores data on the completion of an iteration. 
• The left terminal is used for receiving inputs, and the right terminal is used for sending outputs.

We hope you have understood how to create a shift register in labVIEW from this section.

If you want to enrich your career and become a professional in LabVIEW, then enrol in "LabVIEW Online Training". This course will help you to achieve excellence in this domain.

Initialising a Shift Register

In LabVIEW, initialising a shift register is crucial. You need to wire any value to the left terminal of a loop. 

The image below shows the initialised shift register in LabVIEW.

Below are the reasons that explain why initialising shift registers is essential.

• If you do not initialise the shift register, the loop uses the value written in the last execution.
• If the loop is not executed, the loop uses the default value for the data type.
• For example, the initial value is false if the data type is Boolean and zero if it is numeric.

Using a shift register in a while loop – Example

This section includes an example of finding the accumulated sum of numbers. Here, you will use a shift register in a while loop to find the accumulated sum of numbers from 1 to 10 with multiple iterations.

Let’s walk through the step-by-step procedure for the same.

1. Create a while loop and add a shift register

• First, place a while loop in the block diagram
• Click the border of the loop and add a shift register.

2. Initialise the shift register

• Place a numeric constant in the block diagram
• Wire the numeric constant with the left side terminal of the shift register and set a value in the constant as 0.
• This value is the initial sum for this calculation.

3. Add the Incrementing Logic

• Include an add function in the while loop
• Wire on the left side shift register terminal with the upper input of the add function
• Wire one more numeric constant with the lower input of the add function
• Set the value in the constant as 1. This value will be added to the accumulated sum for every iteration.

4. Set the Loop condition

• Add a comparison operator like greater than or equal inside the while loop.
• Add a numeric constant with the comparator and set the value to 10.
• Wire the iteration terminal of the while loop with this comparator
• Wire the output of the comparator with the stop button.

5. Add a Numeric Indicator

• Add a numeric indicator outside the loop to show the result of the accumulated sum
• Wire the output of the add function with the numeric indicator.

6. Run the LabVIEW VI.

• Click the run button.
• You will see the accumulated sum in the indicator.
• You can change the control values and their accumulated sum in the indicator.

Congrats! You have built a VI to determine LabVIEW's accumulated sum of values.

Stacked Shift Registers

You can use stacked shift registers in LabVIEW to data averages. This section unpacks some crucial information about the stacked shift registers.    

Let’s take a look at the stacked shift registers in this section.

• Stacked shift registers allow access to data from the iterations of the previous loop.
• They can use the values of multiple previous iterations and pass them to the subsequent iterations.

You can configure stacked shift registers in the following way.

• Create a stacked shift register by right-clicking the left or right shift terminal.
• Select ‘add element’ from the shortcut menu.
• You will create an additional terminal on the left side of the loop.
• Set the constant values as shown in the image below and wire them with the add function.
• Wire the output of the add function to a numeric indicator.

Know that stacked shift registers usually exist on the left side of a loop in LabVIEW. That’s because the right side terminal of a shift register passes the data of the current iteration to the next one.

The table below shows the data processing in the shift registers for every iteration.

Iteration	Top left shift register end value	Bottom left shift register end value	Right shift register end value
0	0	1	1
1	1	0	1
2	1	1	2
3	2	1	3
4	3	2	5

The values for both the top and bottom shift registers are set initially. Once the execution starts, the value stored in the top left shift register is passed to the bottom left shift register in the next iteration.

Replacing Shift Registers with Tunnels

Tunnels are the terminals that pass data into and out of data structures. They dont store data between iterations, whereas shift registers support data retention. In other words, shift registers can retain data between iterations.

When you don’t want to transfer values from one iteration to the next, you can replace shift registers with tunnels to pass data between iterations.     

The steps below will help you replace a shift register with a tunnel in LabVIEW.

• Go to the block diagram or VI.
• Right-click on the shift register
• Select the ‘Replace with Tunnels’ option from the shortcut menu.
• Then, you can see two tunnels on the loop on two opposite sides.

Replacing Tunnels with Shift Registers

You can replace Tunnels with shift registers wherever necessary.

The steps below can help you replace a tunnel with a shift register.

• Go to the block diagram or VI.
• Right-click on the tunnel placed inside the loop.
• Choose the ‘replace with Shift Register’ option from the shortcut menu.
• Now, you will see two shift register terminals in the loop on opposite side

Feedback Nodes

Know that a feedback node in LabVIEW works similarly to a shift register used in loops. You can use the feedback node to avoid unnecessarily long wires in loops. Like a shift register, you can use the feedback node to store data.

• A feedback node can be used when a loop completes its iteration and is ready to send the result to the next iteration. 
• It is a part of feedback mechanisms used in labview loops.
• The next iteration reads the data and then writes a new value to the data.
• The data with the new value is sent through the loop again
• This process continues until the completion of the loop execution.

The below image shows the use of a feedback node in a VI.

• Select a Feedback Node on the Structures palette and drag it inside the loop in a block diagram.
• You can place the feedback node on the wire before branching the wire connecting the data to the tunnel. If you do so, the feedback node passes each value to the tunnel.
• Similarly, you place the feedback node on the wire after you branch the wire. If you do so, the feedback node passes each value back to the input of the VI or function. Then, it passes the last value to the tunnel.

Common use cases of shift registers in LabVIEW

Let’s outline the noteworthy use cases of shift registers here.

• Implement state transitions and store state information in state machines.
• Perform signal filtering and processing operations 
• perform mathematical operations on values for multiple iterations
• Enable time delays in data processing
• Execute array operations using the auto-indexing feature.
• Passing data through state machines and event structures
• Collecting and storing data over multiple iterations for in-depth analysis
• Reduce noises in signals by averaging values
• Implement PID controller and feedback loops in control systems
• Store data samples in buffers and align data from multiple sources.

Best practices in using Shift Registers in LabVIEW

This section will unveil the best practices for performance optimisation of shift registers in LabVIEW programs.

• Always initialise shift registers so you can avoid unexpected system behaviour.
• In large programs, use local and variable variables instead of shift registers to minimise memory usage and efficient memory management.
• Ensure the data types connected to the shift register terminals are compatible.
• Documenting the purpose of each register in the VIs is highly required.
• Use data clusters to pass multiple values between iterations
• Fine-tune code organisation and readability      

Summary

• We use shift registers in LabVIEW to store and pass data between iterations of loops or structures.
• Shift registers are similar to the local variables used in text-based programming languages.
• Data enters through the left side of the shift register and is available on the right side for the next iteration.
• You can initialise a shift register with a value outside the loop. If you don’t initialise a register, it takes the last value from the previous execution.
• You can create multiple shift registers within a loop or structure.
• You can use shift registers in state machines to implement state transitions and store state information.

Most Frequently Asked LabVIEW FAQs

1. How long will it take to learn LabVIEW?

You can quickly learn LabVIEW with MindMajix’s LabVIEW training. MindMajix offers 30 hours of live online instructor-led LabVIEW training. We also provide 21 hours of on-demand training with self-paced videos. You can choose the training based on your needs and comfort.

2. Can I initialise a shift register?

Yes, you can initialise a shift register with a specific value before the loop starts. It is highly beneficial for ensuring the correct behaviour of systems or devices.

3. Do you need to make any performance considerations while using shift registers?

Yes, you must be careful about memory usage when using shift registers. In other words, you should avoid using many shift registers.

Related Article - LabVIEW Interview Questions

4. What is the difference between shift registers and local variables in LabVIEW?

You use shift registers within loops, whereas you use local variables outside of the loop. Managing shift registers is simple, no matter how complex the code is, whereas managing local variables is difficult for complex codes.

5. Is it worth learning LabVIEW?

According to AmbitionBox, LabVIEW developers can earn an average of over 5 LPA at the entry-level in India. ZipRecruiter says they can earn an average of around 109k USD in the USA.

Conclusion

Overall, shift registers are powerful tools for managing data flow in loops. They help develop and store state information and create dynamic applications. Understanding LabVIEW's functionalities and best practices is crucial for competent LabVIEW programming.

You can join MindMajix to explore further about LabVIEW programming. At the end of the training, you will elevate your LabVIEW skills to greater heights and become a front-runner in the job market