The INTERNAL_SIGNAL block works with a named internal program variable. It is not part of the physical input or output image.
Typical FBD symbol
IN
INTERNAL_SIGNAL
Q
Typical FBD symbol for INTERNAL_SIGNAL
Inputs
Name
Type
Required
Description
IN
BOOL
No
Optional value to write into the internal signal NAME.
Outputs
Name
Type
Required
Description
Q
BOOL
Yes
The current value of the internal signal NAME.
Parameters
Name
Type
Required
Default
Description
NAME
string
Yes
-
Internal signal name.
Stateful
No, the block does not keep internal state.
Behavior rule
If input IN is connected, the block writes that value to the internal signal named NAME and emits it on Q. If IN is not connected, the block reads the current value of NAME and emits it on Q.
Practical use
intermediate logical signals;
splitting complex diagrams into readable parts;
reusing internal state in different diagram areas.
What to watch
Using the same NAME for multiple writers.
Reading a signal before it is written and ignoring previous-scan behavior.
