This paper proposes a technique which can be applied in the processing operations of programmable logic controllers. It is called multi-rate scanning and originates from multi-rate digital signal processing. It enables the I/O signals processing by using different scanning rates according to their anticipated switching rates. The paper describes how the multi-rate technique can be applied in any type of PLC in order to increase its I/O capacity and share the control tasks. Finally, the utilization of the technique is illustrated by the use of an application example.