Twincat 3: Giving names to array bits

Question

Beginner in the whole PLC stuff, so corrections are welcome.

I am trying to tidy up my project and current situation is thus: I receive 16 byte arrays from modbus. These act as buttons, lights, conveyors what have you in Factory IO.

GAB_FactoryIO_Inputs    AT %I*      :   ARRAY [0..15] OF BYTE;
GAB_FactoryIO_Outputs   AT %Q*      :   ARRAY [0..15] OF BYTE;

So instead of referring to "Start button" with its bit "IO.GAB_FactoryIO_Inputs[0].0" I made a clumsy conversion POU and GVL to go through each bit and give them a new name. So it currently it looks like 200 lines of this:

IO.iSensor10_Capa   :=  IO.GAB_FactoryIO_Inputs[7].3;
IO.iSensor9_Capa    :=  IO.GAB_FactoryIO_Inputs[7].4;
IO.iPositioner_Limit    :=  IO.GAB_FactoryIO_Inputs[7].5;
IO.iPositioner_Clamped  :=  IO.GAB_FactoryIO_Inputs[7].6;
IO.iPick2_Detected  :=  IO.GAB_FactoryIO_Inputs[7].7;
IO.iPick2_MovX  :=  IO.GAB_FactoryIO_Inputs[8].0;
IO.iPick2_MovZ  :=  IO.GAB_FactoryIO_Inputs[8].1;
IO.iPick2_Rot   :=  IO.GAB_FactoryIO_Inputs[8].2;
IO.iPick2_GripRot   :=  IO.GAB_FactoryIO_Inputs[8].3;

And this

iPositioner_Limit   :   BOOL;
iPositioner_Clamped :   BOOL;
iPick2_Detected :   BOOL;
iPick2_MovX :   BOOL;
iPick2_MovZ :   BOOL;   
iPick2_Rot  :   BOOL;   
iPick2_GripRot  :   BOOL;   

It all works as it should, but I cant help to feel its amateurish, unwieldy and slows things down.

I've read about structures, enumeration and alias, and thought structures would be my savior by handily arranging them inside "cabinets", like so:

stCNC.Button1
stCNC.Button3
stCNC.Sensor1

And hidden inside structures would be the conversion between stCNC Sensor1 = IO.GAB_FactoryIO_Inputs[9].4;

But for some reason that doesnt work at all. I'm most likely going at it plain wrong angle, but have no idea what to look for next.

---

EDIT work in progress thus far. Seems like I got the hang of the basics. @kolyur had simple enough example to follow, so I started from there, and progressed towards @Steve and @YAVA examples:

//sending inputs to GVL FactoryIO_Inputs AT %I* : ARRAY [0..15] OF BYTE;
fbMBReadInputs(pDestAddr := ADR(IO.FactoryIO_Inputs), 

//in GVL IO
FactoryIO_Inputs    AT %I*      :   U_UNION2;

//inside S_LIGHTS:
TYPE S_LIGHTS :
STRUCT
    LIGHT0  : BIT;
    LIGHT1  : BIT;
    LIGHT2  : BIT;
    LIGHT3  : BIT;
    LIGHT4  : BIT;
    LIGHT5  : BIT;
    LIGHT6  : BIT;
    LIGHT7  : BIT;
END_STRUCT
END_TYPE

//inside U_UNION1
TYPE U_UNION1 :
UNION
nArray :    ARRAY[0..15] OF BYTE;
sName :     S_NAME;

//Then instantiating in POU
VAR
sLights : S_LIGHTS;
---
sLights.LIGHT1 := TRUE;

Answer 1

You can try to use a UNION. It is basically an "overlay" variable you can place over another variable.

TYPE Test :
UNION
    nARRAY          : ARRAY[0..15] OF BYTE;
    sHumanReadable  : sStruct;    
END_UNION
END_TYPE

UNION on Infosys

Answer 2

A structure could help if you make use of the BIT datatype. BITs address individual bits (unlike BOOLs which require a whole byte) but they can only be used within structures.

TYPE Test
STRUCT
  button1 : BIT;
  button2 : BIT;
  button3 : BIT;
  button4 : BIT;
  sensor1 : BIT;
  sensor2 : BIT;
  sensor3 : BIT;
  sensor4 : BIT;
END_STRUCT
END_TYPE

This structure occupies one byte and you could make an array of them to potentially use in your Modbus routine instead of the byte arrays.

Answer 3

Instead of first linking each IO to a global variable list and then link them to a function block, you could link the symbols directly to an instance of a function block.

For example you make the following function block and put the hardware inputs in the VAR section or you could put them in VAR_INPUT. You could also collect the inputs into a struct as the others suggested and use this struct in the function block.

FUNCTION_BLOCK Picker
VAR
    MoveX AT %I : BOOL;
    MoveY AT %I : BOOL;
    Rotate AT %I : BOOL;
    GripRotate AT %I : BOOL;
END_VAR

Then in your program you make an instance of the picker

PROGRAM MAIN
VAR
    picker1 : Picker;
END_VAR

And then from you system configuration you can link each terminal input directly to the VAR's inside picker1.