Issue
How does scanning frequency and triggers work in EOTE's Modbus TCP and RTU Client drivers for:
- Variables in active screen/active content ID /local scripts - are they polled on when the screen is active even if the scan frequency is set up as let's say 200 ms [external equipment]
- Alarms/Log Logging/Global scripts- are persistent variable polling based on scan frequency?
Product Line
EcoStruxure Operator Terminal Expert
Environment
All HMI hardware families which run on EcoStruxure Operator Terminal Expert: Harmony HMIST6, HMISTM6, HMIGTU, HMIGTUX, HMISTO7, iPC or PC/AT
Resolution
1) For Screen/Content:
Variables that are not on the current screen will not be polled (no requests sent by the driver) and variables that are assigned to screen objects on the currently appearing screen will follow the scan rate defined by the variable declaration.
2) For Alarms:
All the alarm variables will be accessed by the runtime regardless of used or not in screen and will follow the scan rate associated with the Variable declaration.
3) For Periodic Datalogging:
All the datalogging variables will be accessed by the runtime regardless of used or not and will follow the scan rate defined by the variable declaration. The Datalogging frequency will not change the polling rate. The Datalogging frequency only affects the frequency of logging.
NOTES:
-> For Points 1, 2 and 3 above, Runtime will try to optimize (compress/decrease) the communication packet quantity and size. So, if there are many variables with Modbus device addresses that are close to being consecutive, the driver the runtime may send a single request containing a request for a block of consecutive addresses.
-> For some PLCs or Modbus Server devices, some devices addresses may not exist, and the request for a block of addresses may ask for the non-existing Device Addresses (in between what is defined in the EOTE project). If that is the case, the PLC will return Modbus Exception Code 02h ("Illegal Data Address"). To resolve this, change the "Preferred Frame Length" to a smaller number than the maximum (252bytes) until the Exception 02h is no longer returned.
4) For Global Scripts and Screen Scripts
Each external variable used in one or more scripts will result in the driver sending one request packet for each unique register of each Operation. The polling rate is determined by the script line's trigger method (Conditional, Periodic, etc.) - independent of the Variable's Scan Rate in the Variable declaration screen.
