Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

serial read variable length

serial read variable length

serial read variable length

I'm new to LabView (v6) and writing a vi to read an unknown number of bytes from a serial port.  I am using a while loop and would like to exit when the VISA byte count has been zero for some amount of time.

I created a timeout vi, but can't use it as a subvi, because the while loop doesn't "see" the controls in the calling vi.



RE: serial read variable length

One simple and arbitrary way is to start a counter with a 1ms delay (if your can tolerate it). Set a counter timeout threshold and if it reaches it, simply stop the while loop. If within that time the byte count is not 0, then reset the counter and wait for the next 0-byte condition.

It is slightly more complicated if you need a specific timeout period but not that difficult.

Within the while loop, you can use the same counter to indicate that a 0-byte count has been detected. On the first iteration (when 0-byte counter=0) of the 0-byte condition, capture the millisecond tick count into a shift register and on subsequent loops, subtract the current tick count from the original. If it matches or exceeds your timeout time, break out of the loop. Any byte counts detected after the 0-byte condition and before the loop breakout should reset the counter back to 0.

RE: serial read variable length

Thanks for the information.
LabView should be very helpful once I get used to it.
My vi is starting to have several levels of while/for/case structures.  Should I be concerned about getting too deep?

RE: serial read variable length

Yes and no. If this is your first Labview vi, I wouldn't be concerned so much with proper coding technique as I would be learning how things work and getting the program to behave the way you want. As you gain experience, I would then focus on how to write better code. Of course there is probably a school of thought that says you should take the time to learn proper coding technique.

Generally my rule of thumb is to contain the code to what I can fit on my screen without having to use the horizontal or vertical scrollbars too much. If your code starts to get large, look into condensing some code into subroutines. Making Labview code as easy to read as possible will save you time down the line when you have to debug the code.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close