Why does vi execute in HIGHLIGHT mode only? Does not RUN from front panel

Question

This is extraordinarily puzzling to me...
The attached vi sends a serial command to a motor controller.  Command has the form /1V5500P0R, where the /1 means "motor 1",   5500 is the velocity, and the P0  means "rotate positive direction" and R means RUN (do the command).
When I run the VI from the front panel, the motor does not respond.  The correct command string appears in the String indicator box, but, the motor does not turn on.  HOWEVER, when I use either HIGHLIGHT EXECUTION, or I SINGLE STEP through the block diagram, the vi works perfectly.  It issues the correct command the motor runs properly after stepping over VISA WRITE to VISA CLOSE...  The VI accepts any velocity command I want to put in the NUMERIC control on the front panel.
I tried putting the code into a WHILE loop to see if that made any difference...and it does not.
What is happening?
Thanks,
Dave
Attachments:
Simple VISA speed controller forum nov 20.vi ‏12 KB

Answer 1

Hello Angelica,
Your suggestion about use of the WAIT VISA function works, however, I am reluctant to use it because I do not want to slow down the application.  The application accepts two inputs and creates the one serial output, and the faster it does this, the better for my application.
I had no problem running these VI's on my old PC in Labview 2011.  The new PC requires this WAIT function.  There is software provided by the hardware manufacturer to manually send the SERIAL commands, and it works fine on both PCs.
New PC is Intel(R) core(TM) i3-2230 CPU @ 2.2GHz, 3G RAM 64 bit processor and  Labview 2012
Old PC is Intel (R) Pentium (R) M Processor 1.73GHz, .99G RAM, 32 bit processor and Labview 2011
Understand that in the attached VI, only a single serial command is being sent, so, is it possible that backlogging or overloading of the device can occur from a single serial command?  This does not happen with the manufacturer's interface.  The attached vi works with the 10ms wait time. This VI is one of a family of VI's that I wrote and operated in Labview 2011 on the old PC, and all of the worked fine without the WAIT function.  Now, none of them will run in either Labview 2011 or Labview 2012 without the WAIT in the VISA as shown in the attached VI.
Do you really think that the command is being sent too quickly?  The device communicates over the RS485 bus at 9600 baud, 1 Stop bit, No Parity, No flow control.  How can a single string be sent too quickly?
Thank you,
David
Attachments:
Simple VISA speed controller WAIT.vi ‏14 KB