Modbus - How precisely works

[buuuudzik]

I have a question about Modbus. How precisely works on LM?

LM uses user defined interval. But what when I change value? Does user have to wait for checking the change in the system? When the value is sent, immediately or only on interval?

[Erwin van der Zwart]

Hi,

Modbus is polling and not COV so you get the data only on request.

BR,

Erwin

[Daniel]

Hi
Reading data from slave is via pool interval, writing of data is nearly instant.
BR

[buuuudzik]

Currently I am testing communication with recuperator. And I have such variable:

Code:

3x0066 Manual boosting time Manual boosting time / delay (min) Holding register R W 0 - 60 30

This is my configuration from profile:

Code:

{ "bus_address": "14/2/157", "bus_datatype": "uint8", "type": "register", "datatype": "uint16", "address": 66, "name": "Manual boosting time", "units": "min"},

And of course object exists.


But when I try change the variable in LM it is ok, because object changes and stays changed after update. But when I've check this variable via Read test it has value 26. Strange is that LM doesn't update value when it recognize that device has still another. My current setting is 10s interval. There are a lot of errors(what is strange because on read test device responds 100/100 but I unfortunately that see this is normal) but not every interval but only sometimes which after a few hours looks terrible.

[admin]

You need to add "writable": true to your profile entry.

[buuuudzik]

Thanks, this help to change value. I've added this 3 variables to profile a few minutes ago, quickly, by copy another similar values.

But why sometimes variables aren't updated when seems that device is updated because errors aren't every interval but not whole profile is up to date.