IEC 61131-3 FBD is a network of function blocks executed sequentially according to a (their) predefined order. In this section, we define the FBD programming language as a state transition system and propose FBDVerilog translation rules in a bottom-up manner. Explains function block translation, which is a unit of FBDs. Unlike “primitive” function blocks whose translation rules are straightforward, some FBD features cannot be mapped directly.
Function Block Translation
A function block is defined as a tuple composed of Name, input ports IP, output ports OP, and its behavior description BD as defined in Def. 1. IP and OP are the official terms used in IEC 61131-3. The behavior of a function block is defined as a set of predicates and assignments on input and output ports, respectively. A function block is a function from an input variables set, which are assigned to ports of input of the function block, to (usually) one output variable, which is assigned to one output port.
Definition Function Block
A function block is defined as a tuple FB = < Name, IP, OP, BD >, where Name: a name of function block IP: a set of input ports, {ip1, ip2, … , ipn} OP: a set of output ports, {op1} BD: behavioral description Σ(pFB, aFB), where - pFB : a predicate on IP - aFB : assignments on OP Let VFB-I = {v1, v2, ..., vn} be a set of function block input variables which has n input ports, and VFB-O = {vo} be a set of function block output variables. If we define Ii as a set of input domains of the input variable vi (1<=i<=n) and IFB = I1 I2 ... In, and also OFB = Oo in the same way, then a function block is defined as follows: fFB: IFB OFB.