PLC Programming

Controlling a Traffic Signal Unit...
Action Off
The result
PLC_PRG
In our hypothetical situation, night falls after seven TRAFFICSIGNAL cycles, for ten seconds the
TRAFFICSIGNAL turns itself off, then we have daylight again, the traffic light unit turns itself on again,
and the whole process starts again from the beginning. If you like, do another test of the current
version of your program in simulation mode before we go on to create the POU PLC_PRG.
We have defined and correlated the time sequencing of the phases for both sets of traffic lights in the
block SEQUENCE. Since, however, we see the traffic lights system as a module of a bus system, e.g.
CAN bus, we have to make input and output variables available in the block PLC_PRG. We want to
start-up the traffic lights system over an ON switch and we want to send each of the six lamps (each
traffic light red, green, yellow) the corresponding "signal command" for each step of the SEQUENCE.
We are now declaring appropriate Boolean variables for these six outputs and one input, before we
create the programme in the editor, and are allocating them, at the same time, to the corresponding
IEC addresses.
The next step is declare the variables Light1 and Light2 of the type Phases in the declaration editor.
Declaration LIGHT1 and LIGHT2
These deliver the Boolean value of each of the six lights to the above mentioned six outputs for each
step of the block SEQUENCE. We are not, however, declaring the output variables which are
foreseen within the PLC_PRG block but under Resources for Global Variables instead. The Boolean
input variable IN, which is used to set the variable START in the block SEQUENCE to TRUE, can be
set in the same way. ON is also allocated to an IEC address.
Select the tab Resources and open the list Global Variables.
Make the declaration as follows:
3-10 CoDeSys V2.3