Instruction manual

Booleans
48
890USE18300 September 2003
Three-input AND Blocks
Summary A three-input AND block performs a logical AND operation on three Boolean
operational inputs. The output is Boolean true or false, expressed as a value of 1 or
0, respectively. Optionally, you may invert one or more inputs. You may also invert
the value of the output, in which case the action becomes a logical NAND.
Structure of a
Three-input AND
Block
A block diagram for a three-input AND is shown below:
The block has four inputs—one enable input and three operational inputs. The
enable input turns the block on or off. The operational inputs send three Boolean
values to the block. The inputs are ANDed together when the block is enabled, and
the result is a Boolean output.
The checkboxes on the three input lines and the output line provide the mechanism
by which one or more of the input/output values can be inverted. When you click on
one of these boxes, a check mark toggles on or off. When a box is checked, the
value of the associated input or output is inverted—i.e., a 1 becomes a 0, a 0
becomes a 1.
Enable Input An AND block can be enabled either by a Boolean 1 or an always enabled constant.
It can be disabled by a Boolean 0 or an always disabled constant.
If the enable input is a Boolean, it may be produced by:
a digital input from a module on the island
a digital output from the virtual module (See The Virtual Module, p. 28)
an output on the action module (See Using the Action Module as an Input to a
Block, p. 32) written to by the fieldbus master
When the enable input is a Boolean 0 or an always disabled constant, the block is
disabled—the action does not execute and the output is frozen in the state it was in
when the block became disabled. The block continues to process inputs but does
not act on them. If the block becomes enabled, it immediately begins acting on the
latest set of inputs received.
enable
output
operational input 1
operational input 2
operational input 3
AND