METHOD FB_init : BOOL VAR_INPUT bInitRetains : BOOL; // if TRUE, the retain variables are initialized bInCopyCode : BOOL; // if TRUE, the instance afterwards gets moved into the copy code END_VAR Use code with caution.
This method is robust and directly ties the initialization code to the lifecycle of the PLC task itself.
The first scan bit is a versatile tool used in nearly every professional PLC project.
To illustrate the utility of the first scan bit, here are a few common industrial automation use cases: beckhoff first scan bit
The First Scan Bit can be accessed in the PLC program using the following methods:
Understanding the Beckhoff First Scan Bit: Implementation, Use Cases, and Best Practices
Network interfaces, serial buffers, or fieldbus master configurations may contain stale data after a restart. METHOD FB_init : BOOL VAR_INPUT bInitRetains : BOOL;
An compiles only the modified code without stopping the PLC.
PROGRAM MAIN VAR bFirstCycleDone : BOOL := FALSE; END_VAR
The answer lies in a small, single-purpose variable: (or bInit in older TwinCAT 2 nomenclature). Though it appears only once per startup, its impact on system reliability is profound. To illustrate the utility of the first scan
By properly implementing the first scan concept in TwinCAT, you ensure that your Beckhoff industrial PCs boot safely, predictably, and seamlessly transition into active machine control.
Setting default values for variables at startup.