Date Code 20020129
Control Logic
4-23
SEL-387E Instruction Manual
control variables for internal logic, or for creating special customized logic through the use of
SEL
OGIC
control equations.
SEL
OGIC
control equations use logic similar to Boolean algebra logic. A SEL
OGIC
control
equation consists of some combination of Relay Word bits and logical operators that define how
the Relay Word bits are to be evaluated as a group or individually. The Relay Word bits take on
their values of 0 or 1, the operators perform logical operations on these values, and the result is a
logical value of 0 or 1 for the SEL
OGIC
control equation itself. Thus, expressions of assertion or
deassertion apply to the SEL
OGIC
control equations as a whole, as well as to the individual
components of the equation. In the end, the SEL
OGIC
control equation itself is a simple digital
variable having a value of 0 or 1.
SEL
OGIC
Control Equation Logical Operators
In the SEL-387E Relay, there are six logical operators that can be used in SEL
OGIC
control
equations. These operators exist in a hierarchy, from the highest level operator to be processed
to the lowest level operator. Table 4.6 lists these operators in their order of processing.
Table 4.6: SEL
OGIC
Control Equation Operators
Operator Logic
Function
( )
parentheses
! NOT
(negation)
/
rising edge detect
\
falling edge detect
* AND
+ OR
Parentheses Operator, ( )
More than one set of parentheses can be used in a SEL
OGIC
control equation. However,
parentheses cannot be “nested”; you cannot have parentheses within parentheses. The following
is an example:
S1V1 = (IN105 + RB3) * (87R + 87U)
The expressions within the parentheses are evaluated first. The logic determines whether IN105
OR RB3 is asserted and then whether 87R OR 87U is asserted. Assuming that at least one bit
asserts for each pair of parentheses, the equation can now be evaluated: S1V1 = 1*1 = 1. The
equation for S1V1 is thus asserted.
NOT Operator, !
The ! operator performs a simple negation or inversion. On logic diagrams, a small circle on an
input or output line represents this inversion. Whatever the state of the logical quantity to which
it is applied, it simply reverses that state. For example, if 87R is a logical 1, then !87R is a
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