Advanced Modbus driver optimization

[support402]

This feature request comes from a customer via bFO # 98925769 and # 98053984 as well as JIRA CSUP-13309.

The initial request was to optimize the driver to poll outstations as fast as possible (as they used to use a competitors SCADA system which performed that way).  After discussing the pros/cons of that type of architecture, this customer chose to set up a separate channel for "Fast Scan" polling.  Below are comments from the customer regarding this operation.

Switching Outstation to a separate “Fast Scan” channel and allowing IP100 to handle flow of communications helped, but did not completely resolve issues. When switching outstation back to “Normal Scan” channel it does a restart sequence similar to what a refresh does. SE development team should look at improving  how Adv modbus driver handles communication flow and implement a better way of promote / refresh outstations. Outstation retrieval intervals is a great way to optimize points that don’t need to be poll often, but there should also be away to set poll interval to poll data fast as possible and still allow promote scan to work as it was intended to!

[AndrewScott]

To poll a Modbus point as fast as possible set it's Retrieval Interval to Continuous.

Points Used on Generic Modbus Controllers \ Configure Common Point Properties 

Whilst there isn't a specific promoted retrieval interval for continuous, setting the interval to a very small value (e.g. 1ms) will achieve the same effect.

Configuring a Generic Modbus Controller \ Define the Data Retrieval Intervals 

This allows points to be promoted from their normal retrieval interval to 'continuous' using any type of promoted scanning (manual promotion, promote on display, promote after control).

Temporarily Increasing the Scan Rate 

When using two channels for "Normal Scan" and "Fast Scan" how are they switching between channels? Are they using a switched / shared outstation set and switching lines, or are they reconfiguring the outstation (or set) to a different channel? All of these will stop and restart comms with the outstation when switching. Making configuration changes for operational reasons should be avoided as its not efficient.

[sbeadle]

Thank you