Positive Transition Contact

A Positive Transition Contact gives a single one shot pulse when its address reference rises from OFF (logic 0) to ON (logic 1). A Positive Transition Contact is registering the change in status from OFF to ON. The length of the ON status is not relevant.

A Positive Transition Contact condition can be:

A cellular phone keypad key is an example of a Positive Transition Contact. When you push a key a number is displayed on the screen. It does not matter if you push the key quickly or hold it down for several seconds. The number will only appear once on the screen.

The cellular phone registers the transition from no key pressed to a key pressed. The length of time the key is pressed is not relevant. You must release the key and press it again to repeat the number on the cellular phone screen.

During the system scan, a Positive Transition Contact address is evaluated for a transition from OFF to ON. A transition allows power to flow through the Positive Transition Contact for one scan.

At the end of the one scan the Positive Transition Contact is reset to OFF (logic 0) even if the triggering signal stays on. Only after the triggering signal turns from ON back to OFF is there the possibility for the Positive Transition Contact to be activated again with a rise from OFF to ON.


Execution time for Positive and Negative Transition contacts is considerably greater than the execution time for direct and indirect contacts. However, you can decrease the amount of transitional contacts in your program.

Decreasing the Number of Transitional Contacts

You can use the coil of a bit operand to save the positive transition of a contact, and then use the direct contact of the operand in your program.

Rise/Fall Usage Summary

A maximum of 255 Rise/Fall elements is allowed in a project. To ascertain how many elements of each type are in the project, use the Rise/Fall utility on the View menu. The sum of the results must not exceed 255.

If a program exceeds this number, Error 2653 results.

However, in certain cases, the actual compiled number of Rise/Fall elements is greater than the total that is shown in the Summary. Examples are shown below.

Example 1

Example 2



Related Topics

Ladder Elements

Placing Contacts & Coils

Placing a Function Block

Moving elements between nets

Replacing Ladder elements

Ladder Net