Having programmed in C++, I will assume you are familiar with object-oriented programming. Function blocks in CODESYS are really similar to classes in OO languages. So go ahead and create a "motors" class with whatever member variable and methods you wish to use. Instantiate this class for each of your motors (either through individual variables or an array), and make sure whatever code needs to run is called, somehow, from your main program.
I expect the part that will not feel as natural is the part about I/O, and this is what you refer to when you say "assign a variable for each boolean". Because in your project, the (probably BIT rather than BOOL) values you need to read and write have hardware addresses (like %I12.3, %Q3.2). Once you have the classes/instances in place, you still need to tell each instance where to find its own I/O. You would rather not use separate global variables for that, which could lead to code duplication, right?
Here is one way to do it:
Create a structure for each I/O memory block you want to address. The simplest case is all inputs variables are together in I/O memory, and all outputs variables are together too, so that means two structures to define. These structures must match the I/O memory layout bit for bit.
Be careful that TRUE/FALSE I/O is generally exposed as BIT values. When you include consecutive BIT members in your structures, CODESYS will pack them inside bytes (whereas BOOL take up at least one full byte). BIT members are very often needed to ensure a structure matches the true layout of values in I/O memory. Be mindful that all types other than BIT are byte-aligned ; as an example, a lonely BIT variable between to BYTE variables will take up a whole byte.
In your function block, declare variables using your structures as a type, with undefined addresses.
inputs AT %I*: MY_INPUTS_STRUCTURE;
outputs AT %Q*: MY_OUTPUTS_STRUCTURE;
These undefined addresses essentially act as references. Each instance of your function block will receive its own, independent reference. In other for that to work, you have, however, to "map" those undefined addresses to hardware addresses. Under CODESYS this can be done in a couple of ways : you can go to the mapping page of the motor in the project and do it for each variable individually, or you can add a VAR_CONFIG to your project, which will allow you to have one mapping per structure (no need to associate each variable in the structure individually).
Note that when mapping whole structures rather than individual variables, you may have byte order (little-endian vs big-endian) issues to deal with when using multi-byte types if the fieldbus byte order differs from the CPU byte order.
It may seem a bit heavy at first, but once you figure it out it really is not, and it allows you to create function blocks with I/O that can be put in libraries and reused in many projects.
