Soft PLC (Software PLC) is a programmable logic controller based on software, which was born in the late 1990s. It aims to overcome the problems of slow cost improvement and limited technological development caused by the monopoly of manufacturers in traditional PLCs. It achieves the functions of traditional PLCs through the PC platform and a general operating system, follows the IEC61131-3 standard, and supports five programming languages: instruction list (IL), structured text (ST), ladder diagram (LD), etc. Its operating system consists of modules such as IO interface, communication interface, compiler, and error manager, and supports field buses and distributed IO control [2].
Soft PLC relies on an open hardware architecture, is compatible with Windows, Linux, etc. operating systems, and can run on industrial PCs, servers or microcomputers, achieving hardware independence [1] [3]. Its development system has functions such as simulation operation, online modification and network communication, and supports TCP/IP remote monitoring [2]. The system adopts virtualization technology, allowing multiple independent instances to be deployed on the same hardware, reducing downtime [1]. Some solutions combine real-time operating systems (such as SylixOS) to achieve microsecond-level task cycle accuracy and integrate EtherCAT and other industrial protocol kernel drivers to improve communication efficiency [4]. The technical advantages include expandable instruction set, high cost performance, compatibility with standard computer networks and support for user-defined control algorithms.