Build a ladder diagram - CTU counter operation (descending)

The ladder diagram will contain: A counter instruction CTD: C5: 0. Five normally open contacts (XIC): I: 0.0 / 0, I: 0.0 / 1, C5: 0. DN C5: 0. UN, C5: 0.CD. Three coils (OTE): O: 0.0 / 0, O: 0.0 / 1, O: 0.0 / 2. A reset instruction (RES): C5: 0.

The program will do the following:

1.- Each time the I: 0.0 / 0 contact opens and closes, the counter will receive a pulse that will set the CD register and the O: 0.0 / 2 coil high for the duration of the pulse.

2.- At the same time as the above, the accumulator decreases its account by one unit.

3.-Whenever the accumulator is greater than or equal to the preset value, the value of the DN register is one (1), and consequently, the coil O: 0.0 / 0 goes high.

4.- When the accumulator is less than the preset value, the DN register will go low and the coil O: 0.0 / 0 will be deactivated.

5.- The accumulator continues counting down to the value -32 768. After this value, the UN register changes its value from zero (0) to one (1).

6.- To reset the program, it is necessary to close the contact I: 0.0 / 1 to activate the output instruction RES.

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