Execution mode follows the I/O scan mode. In this mode the processor evaluates
the input data stored in memory against the data programmed into the
CPU. The programs are usually set up using ladder networks, where each rung
of the ladder is an instruction for the action to be taken for each given input data
level. The rung instructions are sequentially scanned and the input data evaluated.
The processor can then determine the actions to be taken by the output
modules and puts the data into memory for transfer to the output modules
during the next I/O scan mode