7-14
Inputs, Outputs, Timers, and Other Control Logic
Date Code 20011205
SEL-311A Instruction Manual
Figure 7.13: Latch Control Switch Controlled by a Single Input to Enable/Disable Circuit
Breaker Closing
Note:
Refer to preceding subsection
Optoisolated Inputs
and Figure 7.1. Relay Word bit
IN104 shows the state of optoisolated input IN104 after the input pickup/dropout
debounce timer IN104D. Thus, when using Relay Word bit IN104 in Figure 7.13 and
associated SEL
OGIC
control equations, keep in mind any time delay produced by the
input pickup/dropout debounce timer IN104D.
Feedback Control
Note in Figure 7.13 that the latch control switch output (latch bit LT1) is effectively used as
feedback for SEL
OGIC
control equation settings SET1 and RST1. The feedback of latch bit LT1
“guides” input IN104 to the correct latch control switch input.
If latch bit LT1 = logical 0, input IN104 is routed to setting SET1 (set latch bit LT1):
SET1 = /IN104 * !LT1 = /IN104 * NOT(LT1) = /IN104 * NOT(logical 0)
= /IN104 = rising edge of input IN104
RST1 = /IN104 * LT1 = /IN104 * (logical 0)
=
logical
0
If latch bit LT1 = logical 1, input IN104 is routed to setting RST1 (reset latch bit LT1):
SET1 = /IN104 * !LT1 = /IN104 * NOT(LT1) = /IN104 * NOT(logical 1) =
/IN104 * (logical 0)
=
logical
0
RST1 = /IN104 * LT1 = /IN104 * (logical 1)
= /IN104 = rising edge of input IN104
Rising Edge Operators
Refer to Figure 7.13 and Figure 7.14.
The rising edge operator in front of Relay Word bit IN104 (/IN104) sees a logical 0 to logical 1
transition as a “rising edge,” and /IN104 asserts to logical 1 for one processing interval.
The rising edge operator on input IN104 is necessary because any single assertion of optoisolated
input IN104 by the pushbutton contact will last for at least a few cycles, and each individual
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