TM172 use of PLC variables in HMI expressions

[otrotabi]

According to the online help, expressions can make use of PLC variables:

• You can use PLC variables, target variables, global variables. You can use simple variables, elements of array or structure field.

• Define your expression in ST code, do not enter “=” at the beginning or “;” at the end of the expression.

I tried to define the expression the same way I would do it inside PLC programming and by using @LocalParameters."plcvariablename" format as used when defining edits on the HMI screens

Actually what I am trying to accomplish is to show a static test "Config.Err" or an enumerative corresponding to a USINT variable enumerative on the same place on the screen.

So, how do you do that ? Is it necessary to create a .parx file in the PLC and import it in the HMI ?

[FedericoM · Accepted solution]

Hello,

@syntax is not supported by expressions.

My suggestion, also for data exchange optimization, is to pack boolean info into words (in the programming part), read them in the global script of the HMI and finally unpack them into global hmi variables.

These variables can be used in the expressions...you can find an example in the Parametric AHU template included with ESME HVAC setup

[otrotabi]

Thanks Federico. So the information is not completely accurate then - though it is not wrong -. You still need to use the Video_getParam to import the variables into local variables to use them in the local HMI.

I also tried another approach, by choosing a variable in the visibility field, and then adding "NOT" before the variable. It compiles fine but does not work as expected

Where can I have more information regarding .xml .parx files ? They are mentioned in the literature but since there are no examples I am not sure how to use them.

Regards

[FedericoM]

@syntax is supported in the Visible field, but you can use just variable, you cannot write expressions directly in the field.

Parx file is automatically created inside each project and contains the description of Parameters and Status Variables (the tab LocalParameters shows the info of the related parx files).

I haven't documentation for it...but creating different type of parameters and status, the file structure will become quite clear