Step7: Sectioning a large FB

Let me begin by saying that I am a PLC programming newbie.

Currently I have a multi instance FB, let’s call it Robot, which I am using to control two identical robots. The FB has 28 inputs and 25 outputs, a number of static variables, and consists of 89 networks. What I would like to do is break this large Robot FB into a number of smaller FB or F and then call each one of these smaller function blocks from within the parent Robot FB but avoid passing I/O and static variables around.

Is there a way to read/write to a parent FB I/O and static variables without having to pass them as Input, Output, or In/Out parameters? I know I can load a DB using the OPN instruction but then I’m stuck referencing data using DBX 0.0 instead of descriptive variable names such as “SystemReady”. Perhaps I can pass a UDT around but then in the parent Robot FB I’ll need to copy all the FB I/O to the UDT so it can be passed to child FB calls.

Any help on how to keep this small and tidy would be greatly appreciated. This should be easy to do but I imagine that there something simple that I am overlooking.

Thank you,

AReS

One method as follows:

Each of your child FB's must have exactly the same interface(IN,IN_OUT,OUT,STAT) as the parent FB (i.e. they will start out as a copy of the parent FB but with all the executable code removed. You will add the processing required)

When you call a child FB, use the UC FBx method. The child FB will execute as if had been placed "in-line" inside the calling FB because the UC method does not modify address register 2 or the instance DB. All variables in the interface will be available.

To make things easier to maintain, use S7Guy's method and use a UDT in the stat area. If you need to change the interface, change the UDT (extend it) and it will be updated in all places where it is used. Pass inputs in using logic the conditions the instance DB data before the call, and then drive your outputs from the instance DB after the call.

Whether you consider this "simple" though, is another matter

Here's an example project showing the principle described above.

Wicked!!! This is exactly what I was looking for. I owe you a keg a beer!

AReS

A barrel of Maple syrup will do nicely !