Problem Description

PLC Program
Here is PLC program to Control Traffic Lights, along with program explanation and run time test cases.
List of Inputs and Outputs
I:1/0
= Start 
(Input)
I:1/1
= Stop
(Input)
B3:0/0 = Latched Coil Bit
(Bit)
T4:0
= Timer to update output sequence (Timer)
SQO
= Sequencer output
(Sequencer)
O:2/0
= North-South Green Light
(Output)
O:2/1
= North-South Yellow Light
(Output)
O:2/2
= North-South Red Light
(Output)
O:2/3
= East-West Green Light
(Output)
O:2/4
= East-West Yellow Light
(Output)
O:2/5
= East-West Red Light
(Output)

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Ladder
 
Diagram
 
to
 
control
 
Traffic
 
Light
Program Description

RUNG000 again here is for Master Start and Stop the process.

File; #N7:0 and File length is 10, hence output sequence is varied from N7:0 to N7:10 with each input.

Destination is set to O:2 hence with each transition, N7:0 to N7:10 are moved to O:2 with masking.

O:2/0 to O:2/5 are used as the output address to Traffic Lights and hence Mask has value 003Fh which
means data flow of N7:0/0…N7:10/0 to N7:0/5…N7:10/5 is passed and the remaining N7:0/6…N7:10/6 to
N7:0/15…N7:10/15 are blocked.

Control parameters are assigned to register R6:0.

Sequence of traffic lights to be operated are stored in the registers from N7:0 to N7:10 as following.

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
Time base is set to 4secs, hence after every 4secs, output sequence is changed to its next register pattern
outputs which is then transferred to O:2 and O:2/0 to O:2/5 are energized accordingly.

As we can see, from N7:1 to N7:4 have the same bit pattern. So, these bits are set to 1 for 4 cycles that is
16secs. These bits are used for South-North Green light and East-West Red light.

Similarly the entire sequence is followed.

When Stop I:1/1 is pressed, Position is reset to 0 and all the outputs are de-energized.