Here is the latest in case anyone else runs into this: So, after claiming otherwise for more than a week, Unitronics support is now saying that in fact ANY and ALL Modbus errors cause the master to enforce this 3 second messaging suspension.  So even a -11 timeout error (or anything else) will cause this 3 second lockout and the -2 error code just reports that the master is in this suspension period.  This matches the results of my testing, and I really could not understand how it could be any other way.  They claim that attempting a transaction and receiving the -2 error code does not reset the 3 second suspension (although I'm not completely convinced of this - will need to try it for myself since I'm fairly sure I have results that prove otherwise). There is no indicator or flag you can use to check the state of the Master (which is a bit lacking) - the only way to check the state is to try another transaction and see if it works. They did specifically say that this suspension applying to all errors is the case when you are using serial comms (Modbus RTU), so it may well not be the case if you are using Modbus TCP.  Not sure? Would be awfully nice if this stuff was properly documented in the help file ....

Gracias!.

Thanks Saragani.   All worked

Hello; I am new to the forum and I have the following question; I have to implement a Unistream USC-B5-TR22 on a CAN Bus and I can see that this PLC has a sniffer function, I have tried to obtain information regarding how to use it and implement it in a project but I have not found it or I have been searching wrong, I Can you help by telling me where to find information such as videos, tutorials, etc. I would be grateful. Greetings Guille71

Does anyone know of any companies that do repair and mobile SERVICE in Michigan for Unitronics?