User guide

Chapter 5
Ladder Program Basics
5–3
During controller operation, the processor determines the on/off state of the
bits in the data files, evaluates the rung logic, and changes the state of the
outputs according to the logical continuity of rungs. More specifically, input
instructions set up the conditions under which the processor will make an
output instruction true or false. These conditions are:
• When the processor finds a continuous path of true input instructions in a
rung, the OTE output instruction will become (or remain) true. We then
say that “rung conditions are true.”
• When the processor does not find a continuous path of true input
instructions in a rung, the OTE output instruction will become (or remain)
false. We then say that “rung conditions are false.”
The figure below shows the on/off state of output B3/12 as determined by the
changing states of the inputs in the rung.
B3
10
B3
11
XIC XIO OTE
Input Instructions Output Instructions
B3
12
Inputs Output Bit Status
Time XIC XIO OTE XIC XIO OTE
t
1
(initial) False True False 0 0 0
t
2
True
True Goes True 1 0 1
t
3
True False Goes False 1 1 0
t
4
False False Remains False 0 1 0
Logical Continuity