Spurious commands delaying read time

I thought this particular problem had been cured, but it seems to have come back. I’ve been using a Modbus development tool to read ADC output values without a problem. I've written a small vi which should do the same thing. It runs on the same PC and uses the same COM port. Obviously I have to close the Modbus programme to release the COM port for LabView. The vi runs fine, but data only appears on the front panel every 8 seconds.
Putting in a 500ms delay in MB Serial Receive.vi improves the response time to around 500ms, but I need 100ms. A shorter delay just results in 8 second refresh times again. The 500ms delay workaround has been implemented in the vi Reverse Power by putting the delay in a FOR Loop.
I’ve created log files looking at the data flows and they are very different between the dvelopment tool and the vi. I’ve attached these. For the Modbus development tool it can be seen that at line 130 that the data is written as a single word, and immediately received as a single word.
For the vi, there’s a lot of communication activity at the start that as a novice I don’t begin to understand, but at line 35 the data gets written. However, the read operation doesn’t take place until line 68.
I've attached the vi, Reverse Power, and the sub-vi's, and the log files. I would appreciate any ideas on how to solve this problem. Thank you.
Attachments:
Modbus Spurious Commands.zip ‏649 KB

Hello Placebo,
Thank you for your post on this forum.
I have had a look at your code and I need to ask you for some clarifications to better understand the issue. From your post I could gather that you were experiencing similar issues before. Is this the case? Did you manage to solve it at that time?
Moreover, it would be hard for me to test your code since I don't have the hardware you are currently using. It might be useful to give me some more information on what you are trying to do.
The link below might help you if you have not seen it before:
http://zone.ni.com/devzone/cda/tut/p/id/7675
Have a look to make sure you have implemented your VIs properly.
Many thanks,
Shalini B
Applications Engineer
National Instruments UK & Ireland

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