Modbus Serial Comm

[petersrj]

I am new with LabView so I need some general/basic guidance.

I have a serial Modbus based project.  The project needs to repeatedly make 3 calls each getting 64 registers which then need to be processed (read only for right now).  I need to update ~every 3 seconds or so.  I am using the MB Serial Master Query.  I am getting timeout errors which I want to minimize/manage.  Here are my questions:

1.  I am using a timed loop with three sub-diagrams.  Is this the best way?

2.  Is there a way to know when one of the calls ends (to control time in between calls)?

Thank you for your help.

[K C]

Hi,

Before you can use ModBus you have to be sure that your hardware layer is OK.

What interface are you using. Do you know it is OK ?

Does your ModBus device supports the ModBus Loopback command ?

Kees

[petersrj]

KC,

Thank you for the reply.  The hardware is a gas analyzer that we are developing.

I probably should have clarified some things.  I can get the Modbus communication to work.  It might work for 2 minutes and then time out.  It might work for an hour and time out.  So hardware is good, setup of registers, comm parameters are good, etc.

I have use a third part software (Modscan) to test the Modbus setup and have had no issues with this.

I am wondering if there needs to be delays in-between each of the read commands?  If so, do I do it in the loop?  What parameters control the delay between read commands?  Is there a way to get know when one command is done so I can initiate the next command? 

[K C]

Hi,

Ok, post your vi here.  I will have a look at it.

Kees