The paper describes the design and implementation of a robot control system on a hardware platform based on a Programmable Logic Controller (PLC). The controlled robot is a 4 degrees of freedom (DOF) manipulator with a closed kinematic chain, designed for high-performance pick and place applications in a packaging workcell. The control software is fully developed on a commercial PLC system, using its standard programming tools and the multi-tasking features of its operating system. In particular, the paper analyse in detail the drawbacks and the advantages related to the choice of standard PLCs in this kind of applications, compared to the much common choice of specialized hardware or industrial personal computers, with particular emphasis on the computational performances obtained with the proposed control architecture.