Lenze DDS v2.0 - Manual (Page 7)

Introduction to IEC 61131-3 programming
The software model
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DDS-IEC61131 EN 2.0
2.2.2 Function blocks
The IEC 61131-3 standard uses standard functions and function blocks to standardize typical PLC
functions. This ” Standard library” is an important basis for uniform, manufacturer-independent
programming of PLC systems.
Function blocks (FBs) can be compared with integrated circuits, which include a certain control
function. They are used to set inputs/outputs and internal variables. The status of a function block
request is saved from cycle to cycle. Only the input and output variables of the function can be
addressed by the request program. A function block can also be called by another function block.
Instancing of function blocks
IEC 61131-3 provides the instancing of function blocks. An instance is a structure which saves all
internal input and output variables when a function block is called.
A program which calls FB1 three times has three instances of FB1, one for each call. The program
can thus be evaluated precisely on request and without any side effects. Please observe that all
instances use the same program code, i.e. changes of the program code have the same effect on
al three requests.
Software tools like the Drive PLC Developer Studio help instancing by means of an automatic
declaration: An instance name is specified for an FB call. This name manages the data structure of
the call.
Overview: IEC 61131-3 standard function blocks
Bistable function blocks
SR/RS
Bistable function block (dominant set/reset)
SEMA Software semaphore (interruptable)
Signal detection
R_TRIG/F_TRIG
Detector of rising/falling signals
Counters
CTU/CTD
Up-counter/down-counter
CTUD Up and down counter
Timers
TP
Pulse encoder
TON/TOF Timer on-delay/timer off-delay
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