Instruction manual

Booleans
890USE18300 September 2003 47
Operational
Inputs
Every XOR block requires two operational input values. These inputs may come
from some combination of:
constant values
digital inputs from modules on the island
digital outputs 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
if the XOR is the second block in a nested reflex action (See Nesting Two Reflex
Blocks, p. 36), an operational input may be the output from the first reflex block
Physical Output The output from an XOR block is a Boolean true (1) or false (0), as shown in the truth
tables that follow. The physical output (See Configuring the Physical Output from a
Reflex Block, p. 27) needs to be mapped to an action module:
The action module may be a digital output module on the island bus. In this case,
you need to specify one of the digital output channels as the destination for the
reflex output.
If the XOR is the first block in a nested reflex action, the action module needs to
be the same as the one specified for the second reflex block. Specify the channel
as None.
When the output from a block is mapped to a channel on a digital output module,
that channel becomes dedicated to the reflex action and can no longer use data from
the fieldbus master to update its field device. The fieldbus master still has the ability
to write data to this bit address in the NIM, and the reflex action editor lets you use
this data from the fieldbus master as an input to the block.
Truth Table In its simplest form, a standard XOR block looks like this:
and an inverted XOR (an XNOR) block looks like this:
The following truth table shows the possible outputs:
If input 1 is: and input 2 is: then the standard output is: and the inverted output is:
00 0 1
01 1 0
10 1 0
11 0 1
input 1
input 2
output
input 1
input 2
output