Siemens S7 FB/FC Declarations.

I am reletively new to Siemens S7 & would like someone to provide me with a declatration table for designing Function Blocks, Parameter Assignable Functions. i know that an Input is "IN" & an Output is "Out", but I'm not sure about the other operands like timers, counters, positive edges etc. In other words what are the basic 'rules' for declaring?

The Help in Simatic manager contains a lot of information.

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