Extended relay ladder logic for programmable logic controllers

A computer readable storage device used to direct an on-site computer to implement a software system for programming controllers using a software package of the type utilizing relay ladder logic to represent control programs, the control program executable by the controller to control the operation of one or more devices, the improvement which comprises:

• (a) translating programming information into a graphical relay ladder logic diagram, said diagram including a contact and a coil;
• (b) replacing a coil with an ACTION block, said ACTION block containing at least one general expression;
• and
• (c) evaluating said general expression within said ACTION block when the left side of said ACTION block is energized.

In a computer implemented software system for programming controllers using a software package of the type utilizing relay ladder logic to represent control programs, the control program executable by the controller to control the operation of one or more devices, the improvement which comprises:

• (a) means for translating programming information into a relay ladder diagram, said relay ladder diagram including at least one coil and at least one contact;
• (b) means for displaying the relay ladder diagram on a digital computer video display screen during programming of the controlled application;
• (c) means for replacing a coil with an ACTION block, said ACTION block containing at least one general expression;
• (d) means for evaluating said general expression within said ACTION block when the left side of said ACTION block is energized.