Can function block instances be passed as inputs to other blocks?
Yes if function block FB1 is passed as an input to a second function block FB2, it is possible to invoke the function block FB1 within the body of FB2. Any input parameters of FB1 not defined in the invocation call within FB2 will take values defined by earlier invocations of FB1 made outside of FB2. Function block instances should be passed as VAR_IN_OUT parameters otherwise the values produced within the internal invocation will not be preserved. • Are the assignments of inputs and outputs to programs at the resource level fixed or can they change dynamically? They are fixed. Programs are the highest level IEC 61131-3 programmable organisation unit. It is not possible to have language statements outside of a program. In a resource declaration it is only possible to assign input and output variables to the program interface. If it is necessary to change the inputs used by part of a program, then all inputs concerned should be passed to the program and any dynamic selection of particul
