Reconfigurable State Machine Module for FPGA-Based Programmable Controllers

Existing field-programmable gate array (FPGA) implementations of programmable logic controllers (PLCs) still suffer from limited speed compared to high-performance industrial controllers or restricted programming flexibility, if a control algorithm is directly mapped into hardware without a CPU. In this article, a new approach is proposed that may mitigate these drawbacks. The approach is to integrate with an FPGA-based PLC system, a configurable hardware module, called the RSM, that is capable of implementing some combinational or sequential control algorithms on a hardware basis. The key idea behind the RSM module is that the actual functionality of the module is not statically set during FPGA project implementation by FPGA synthesis tools, but it can be established at any time during FPGA-based PLC system operation. Since the FPGA synthesis tools are not needed, this approach combines high programming flexibility with the high performance ensured by hardware implementation. This article presents a detailed architecture of the RSM module, which is capable of implementing up to 12 Boolean functions of up to 12 variables, or a state machine with up to 12 state variables, along with some IEC 61131-3-compliant function blocks. The RSM can find application in cases where high-speed implementation of logic control algorithms is needed, whereas the other less time-demanding tasks can be executed by the CPU.