Programmable Logic Controllers (PLCs) are one of the core devices in industrial automation and are key applications that enable factories to operate in an automated manner. PLCs are typically modular systems composed of multiple modules, specifically designed to perform logic control, sequential control, timing control, counting control, and other operations. This article will introduce the application of PLCs in industrial automation, as well as related solutions specifically launched by STMicroelectronics (ST) for PLC applications.
Controlling industrial automation equipment through logic
PLCs are widely used in various automation systems, consisting of a control unit (commonly referred to as the Central Processing Unit, CPU) and multiple input/output or other functional modules (expansion modules). The control unit communicates with expansion modules via a dedicated bus (often a customer-specific bus called the backplane interface). The control unit operates cyclically and periodically exchanges data with the expansion modules. The input/output modules interface with the plant processing side, providing information on various physical variables detected by sensors on one side and allowing interaction with the automation process by driving different actuators on the other side. Each module needs to be integrated into the complete automation system to provide connectivity for various fieldbuses and industrial Ethernet.
The primary functions of PLCs in industrial automation include controlling equipment operation through logic control based on pre-written logic programs, such as deciding whether to start or stop a machine based on sensor input. In sequential control, PLCs can execute operations in a specific order on an automated production line, ensuring that each process is completed on time.
Additionally, the timers and counters within the PLC can be used for precise time control and material counting. Modern PLCs also have analog input and output capabilities, allowing them to process analog signals such as temperature and pressure. PLCs can also exchange data with other devices through various communication protocols, enabling remote monitoring and control. They are also capable of detecting and diagnosing system faults and, when possible, automatically recovering operations.
PLCs can control the coordinated operation of various automated equipment
PLCs are widely used in automated production lines to control the coordinated operation of various equipment, thereby improving production efficiency. In industries such as chemical processing, food, and beverages, PLCs can be used to control various parameters in the production process, such as temperature, pressure, and liquid levels. Additionally, PLCs can be used for the operational control of machinery, such as CNC machines and packaging machinery, ensuring their precise operation.
PLCs can also be applied in building automation, controlling systems such as HVAC, lighting, and security. In water treatment and wastewater treatment systems, PLCs can control pumps, valves, and other equipment to achieve automated operation. In energy management systems, PLCs can be used to monitor and control the distribution and consumption of energy, achieving energy-saving effects. The flexibility and reliability of PLCs make them an indispensable component in industrial automation, capable of adapting to various complex control needs.
In fieldbus and industrial Ethernet applications, wired communication technology is widely used in Industry 4.0 and Industrial IoT applications. This technology is continuously evolving, transitioning from traditional fieldbus systems to Ethernet-based buses to connect human-machine interfaces (HMIs), programmable logic controllers, machines, I/Os, drives, actuators, and sensors.
HMIs help us effectively control equipment and make decisions based on machine feedback. This interface can range from simple displays mounted directly on machines for factory automation to multi-touch display panels used to control entire production lines. Additionally, to achieve Industry 4.0, PLCs can use the IO-Link communication network (IEC 61131-9) for bidirectional point-to-point data connectivity down to the actuator and sensor level, supporting data preprocessing, sensor parameter tuning, and advanced diagnostics.
In digital I/O module applications, input/output (I/O) modules collect data from input devices, including proximity, pressure, temperature sensors, and push buttons, and control actuators such as valves, relays, and lamps (output devices). These modules can be added to PLC control cabinets or integrated into the manufacturing equipment of the factory floor.
Within a PLC, the PLC control unit is the primary building block that processes data from input devices and controls the output. It can be integrated with I/O modules to provide the required functionalities. The PLC control unit also supports connectivity to various fieldbuses including PROFIBUS, Modbus, and CAN open, industrial Ethernet such as Profinet, EtherCAT, wireless technologies, and the system’s backplane bus.
High-cost performance and energy-efficient microprocessor
ST has introduced a PLC solution based on the STM32MP135 for industrial automation applications. The STM32MP135 is a high-performance microprocessor (MPU) featuring a 32-bit Arm Cortex-A7@1GHz, dual Ethernet, dual CAN-FD, as well as an 8-channel isolated high-side intelligent power switch (IPS) for digital outputs and a 4-channel isolated low-side IPS, along with 12 isolated digital inputs. By using the LogicLAB PLC runtime based on the ThreadX RTOS, the PLC reference solution is aimed at high-performance applications and markets. This reference platform offers popular industrial field buses such as one EtherCAT master port, one Ethernet port, RS-232/RS-485/ModBus interface, CAN interface, USB, and MicroSD™ card interface, among others.
The STM32MP135 microprocessor series also features a dedicated LCD-TFT parallel display interface, a 16-bit parallel camera interface, and dual Ethernet ports. It offers high cost-performance, efficient processing capabilities, and certified security. The STM32MP135 series includes advanced security encryption features, such as a cryptographic accelerator that enhances hardware robustness, memory protection to against illegal access control, and support for code isolation mechanisms, providing runtime protection. It includes multiple features to ensure platform authentication throughout the product lifecycle and a complete security ecosystem.
The STM32MP135 MPU is specifically designed for entry-level Linux, bare-metal, or RTOS system designs and is pre-integrated with Microsoft Azure RTOS. The STM32MP135 series is available in three different packages, supporting cost-effective PCB architecture. The STM32MP1 series is a general-purpose microprocessor aimed at various industrial applications, including industrial and factory automation, metering, smart homes, point of sale, medical and healthcare, and electric vehicle chargers.
For PLC applications, the STM32MP135 PLC reference design platform, customized by software partner Shanghai Nxtrol technology based on LogicLAB Runtime, provides customers with an open, high real-time, and high-performance solution. The STM32MP135 PLC reference design platform supports five programming languages defined by IEC61131-3, including Ladder Diagram (LD), Function Block Diagram (FBD), Structured Text (ST), Sequential Function Chart (SFC), and Instruction List (IL). Additionally, it features multiple PLC memory areas, including a 16MB program area, a 32MB data area, and a 128KB non-volatile memory area. The execution performance of basic PLC instructions is only 4ns, with a high-speed I/O interrupt response time of less than 1µs, and an interrupt task response time of less than 10µs. The recommended minimum cycle for EtherCAT master (with DC enabled) is 250µs (for less than 8 slaves), 500µs (for less than 16 slaves), and 1ms (for less than 32 slaves). The maximum number of motion control axes is 32 (including pulse axes and virtual axes). It supports IEC61131-3 standard function and function block libraries, high-performance PID libraries, bus communication libraries, PLCopen motion control libraries, MQTT client libraries, JSON format libraries, COM serial free protocol libraries, TCPUDP free protocol libraries, CAN free protocol libraries, file system libraries, and other functional instruction libraries.
The STM32MP1 series MPU can also be paired with the STPMIC1, a dedicated power management IC (PMIC) for battery-powered applications. The STPMIC1 is a highly integrated power management IC designed specifically for applications based on highly integrated application processors, meeting their low power consumption and high-efficiency needs. The device integrates advanced low-power features that can be controlled by the host processor via I2C and IO interfaces.
The STPMIC1 regulators are designed to supply power to the application processors and external system peripherals such as DDR, flash memories, and other system devices. The boost converter can power up to three USB ports (two 500 mA host USB and one 100 mA USB OTG). This converter employs an advanced bypass architecture to smoothly regulate the USB port’s VBUS from both battery and low-cost consumer-grade 5 V AC-DC adapters.
The four buck SMPS of the STPMIC1 are optimized for a low-power mode with a smooth transition from PFM to PWM, and it features advanced PWM synchronization technique with an integrated PLL, aimed at achieving better noise performance (EMI performance). This allows for excellent transient response and output voltage accuracy under more relaxed operating conditions, as well as high full-range efficiency (η up to 90%).
High-performance microprocessor with NPU accelerator
Additionally, STMicroelectronics has introduced a PLC solution based on the STM32MP257, a latest high-performance MPU featuring dual 64-bit Arm Cortex-A35@1.5GHz, 32-bit Cortex-M33@400MHz, 3x Ethernet (2+1 switch), 3x FD-CAN, and more. It includes an 8-channel isolated high-side IPS and a 4-channel isolated low-side IPS for digital outputs, as well as 12 isolated digital inputs. By utilizing the mainstream CodeSys PLC runtime on a Linux OS, the PLC reference solution is aimed at mid-to-high performance applications and markets. This reference platform offers popular industrial field buses such as one EtherCAT master port, two Ethernet ports, RS-232/RS-485/ModBus interfaces, CAN interface, USB, microSD™ card interface, and more.
The STM32MP257 application processor features a total of 3 Ethernet ports, 3 FD-CAN interfaces, H.264 encoding/decoding, a 3D GPU, AI/NN capabilities, LVDS/DSI display interfaces, and security features. The STM32MP257 also provides a dedicated evaluation board, the STM32MP257F-EV1, to help customers get started with their designs smoothly. This product includes an NPU accelerator and can flexibly run AI applications on either the CPU, GPU, or NPU, offering excellent edge AI capabilities. Additionally, it supports high-end edge computing applications like machine vision through its multimedia capabilities, all enabled by ST's comprehensive edge AI ecosystem.
The STM32MP2 series is a versatile microprocessor, catering to different market segments and industrial applications, including electric vehicle chargers, industrial and factory automation, smart homes, metering, and more.
The STM32MP2 series offers enhanced security with certified advanced security features that support secure functions for IoT and industrial applications (targeting SESIP3 certification, based on Cortex®-A and Cortex®-M TrustZone® technology, secure isolation for edge confidential computing). It also supports a rich ecosystem, helping customers accelerate development through the mainstream open-source Linux distribution OpenSTLinux based on Yocto, enabling quick and easy software application porting.
The STM32MP2 series also introduces an Android distribution and provides the STM32Cube toolset, including STM32CubeMX (pins and clocks configuration, DRAM interface tuning tool, code generation for Linux based on Arm Cortex®-A35 and STM32Cube firmware based on Arm Cortex®-M33), GCC-based IDEs, and STM32CubeProgrammer with signing tools.
Due to its high level of integration, the STM32MP2 series supports packaging compatible with low-cost PCB technologies (down to 4-layer plated-through hole PTH-PCBs), and with a dedicated power management IC (PMIC), users can achieve an optimized Bill of Materials (BOM). The STM32MP2 series also has a broad third-party ecosystem with support for Buildroot and OpenWRT through partner collaboration. Partners provide System on Module (SoM) solutions based on the STM32MP2 series, with ST-authorized partners including UI tool providers, secure software providers, training, and software services.
Conclusion
As a core component of industrial automation systems, PLCs provide efficient, stable, and flexible solutions for various industrial applications. With its powerful logic control, sequential control, analog processing, and data communication capabilities, PLCs not only automate production processes but also significantly improve production efficiency and product quality. With the advancement of Industry 4.0 and smart manufacturing, PLCs will play an even more critical role in future industrial automation, helping enterprises achieve digital transformation and sustainable development. The high-performance microprocessor PLC solutions offered by ST, featuring high cost-effectiveness, comprehensive functionality, and efficiency, will be an ideal choice for developing PLC-related applications.