Instruction manual

Booleans
46
890USE18300 September 2003
XOR Blocks
Summary An XOR block performs an exclusive-OR operation on two Boolean operational
inputs. The output from the block is Boolean true or false, expressed as a value of
1 or 0, respectively. You may invert the value of the output, in which case the action
becomes an exclusive-NOR (XNOR).
Structure of an
XOR Block
An XOR block diagram is shown below:
The block has three inputs—one enable input and two operational inputs. The
enable input turns the XOR block on or off. The operational inputs send two Boolean
values to the block. The inputs are XORed with each other when the block is
enabled, and the result is a Boolean output.
The checkbox on the output line provides the mechanism by which the output value
may be inverted. When you click on this box, a check mark toggles on or off. When
the box is checked, the value of the associated output is inverted—i.e., a 1 becomes
a 0, a 0 becomes a 1.
Enable Input An XOR 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
input 1
input 2
XOR