Problem with modbus connection with Unitronic V-560

We are trying to connect Ignition with Modbus TCP to a Unitronics V-560 PLC.

Most of the communication is working, but we have to set the settings Max Holding Register Per Request and Max Input Registers per Request to 2 (default is 125). If we enter larger values, some double registrers return strange, long values.

In the future we need to connect to 10 PLC’s. Does this setting influence the performance of the system? We are already experiencing long loading times.

We are using Ignition v7.9. and v5.9.0 of the Modbus Driver.

Are you sure you can only use a max of 2 registers per request with these?

It may be that what you actually need is to turn the “Span Gaps” setting off and that you’re achieving the same effect by coincidence by reducing the max requests so much.

Both settings impact performance negatively, but only in the sense that the polling throughput you can achieve with each device will be lower. You’re not going to meaningfully impact the overall performance of the gateway with just 10 devices.

We tried to change the setting from 2 to 8 Or 215 (default), by changing this setting we got very strange values.
We tried the span gap setting also but it didn’t have any positieve influence.

It looks like the driver has problems with getting larger data blocks.

[quote=“MVE”]We tried to change the setting from 2 to 8 Or 215 (default), by changing this setting we got very strange values.
We tried the span gap setting also but it didn’t have any positieve influence.

It looks like the driver has problems with getting larger data blocks.[/quote]

Are you the same poster or same company?

Anyway, maybe you can get a Wireshark capture and/or call into support to look at the issue closer. It wouldn’t be the first time I’ve seen a device with a poor Modbus implementation that, for example, starts returning bogus values when you read across some address boundary or read blocks of addresses containing a mix of valid and invalid addresses.

@MVE, @dvorstenbosch - Did either of you resolve these issues? I am having similar issues and would love to know if you were able to get this figured out.

Thanks for any help!

Finally got this going

Hoping this will save someone extra work.