Programming methods of IEC 61131-3
The IEC61131-3 standard defines 5 programming methods for PLCs:
- Ladder diagrem (LD)
- Functional block diagram (FBD)
- Structured text (ST)
- Instruction list (IL)
- Sequential function chart (SFC)
Functional block diagram (FBD)
FBD (or FUPLA) is a programming language based on predefined blocks of code. Each block has its specific function and its inputs (temperature value, switch signal) and outputs (switch command, regulation etc.). The control logic itself is then created in a clear graphic interface simply by connecting the blocks and variables. Mervis IDE features a large library of default function blocks covering an absolute most of all basic PLC operations, such as mathematical functions (sum, multiplication, comparison), control loops (hysteresis, three-way valves), counters, time schedulers and much more. You can also create more complex blocks by connecting several other blocks. FBD is thus suitable for users without any deeper programming knowledge.
Structured text (ST)
The ST language is based on a structured text able to express complex functions by only a handful of lines of text code. The ST is useful mainly for experienced users and programming extensive complex projects. ST can be also used to create custom function blocks if needed.
