AND starts with two inputs. Its properties let you add inputs and remove unconnected ones while keeping at least two. Q is TRUE when all connected inputs are TRUE. An unconnected input is TRUE, marked on; with no connections Q=TRUE.
Typical FBD symbol
IN1
IN2
AND
Q
Typical FBD symbol for AND
Inputs
Name
Type
Required
Description
IN1
BOOL
No
The first boolean condition.
IN2
BOOL
No
The second boolean condition.
Outputs
Name
Type
Required
Description
Q
BOOL
Yes
The logical AND result.
Stateful
No, the block does not keep internal state.
Internal state allows a block to account for previous input values, elapsed time, or an accumulated result.
Behavior rule
Q = IN1 AND IN2 AND …; unconnected input = TRUE
Truth table
IN1
IN2
Q
FALSE
FALSE
FALSE
FALSE
TRUE
FALSE
TRUE
FALSE
FALSE
TRUE
TRUE
TRUE
Practical use
permit start only when the start button is pressed and the safety door is closed;
What to watch
Treating a connected FALSE as an unused input: it is evaluated and makes Q FALSE.
Expecting FALSE with no connections: every unconnected AND input is TRUE.
