Aiding Developers With Minimal Latency and Maximum Reliability
Many industries rely on control systems with minimal latency and maximum reliability. These industries, such as robotics, motor control, power distribution, automotive, electric vehicles, power backup, and so on, are steadily upgrading legacy analog systems to modern real-time and closed-loop control systems powered by Microcontrollers (MCUs) and Digital Signal Controllers (DSCs). The advantages of this modernization effort include greater efficiency, safety, enhanced capability, and future-proofing. These benefits are only possible, however, if extremely reliable MCUs/DSCs equipped with diverse and capable peripherals are available, and if development resources are also available to ease the burdens of development for stringent Functional Safety and Automotive criteria.
There are many challenges for MCUs/DSCs and developers when approaching real-time and closed-loop control systems, and Microchip has developed a robust range of MCU/DSC families and development resources to aid developers in overcoming these hurdles. This article aims to educate designers and developers on several of the challenges associated with these critical systems and Microchip’s cutting-edge solutions for mitigating such challenges.
The Issues: Real-Time Reliability and Closed-Loop Control
Real-time/closed-loop control requirements are incredibly stringent on reliability and deterministic behavior. Applications with these specifications tend to be used for critical industrial and automotive systems, so the ability of electronics to operate in a wide range of environments (including extreme environments) is essential. Most MCUs/DSCs (and most electronics, for that matter) are not able to reliably operate over a reasonable lifetime while experiencing temperature extremes, substantial shock/vibrations, high levels of Electromagnetic Interference (EMI), or undergoing significant g-forces.
Real-time reliability also means that the electronics can respond with very-low latency to external inputs and complete computations/operations successfully in order to deliver the correct output controls and data. There are many factors, including built-in redundancy, error-correction, and more, that are necessary for an MCU/DSC to be able to operate as a closed-loop controller. This is especially challenging as these MCUs/DSCs are also often tasked with non-critical functions. Though these non-critical functions may not be mission-critical, they may be required to make a product competitive or provide important auxiliary functions. Unfortunately, real-time MCUs/DSCs have limited processing power, especially low-power 8-bit variants, and typically critical and non-critical functions must share resources. This burden often means embedded developers must expend substantial development resources to balance processor resources carefully.
Moreover, the complex algorithms and advanced calculations needed to provide real-time/closed-loop control are generally complex to develop already, and this challenge is exacerbated by the additional need to balance processor load efficiently. Ensuring system stability with extreme operating conditions and a high level of performance demand is a multifaceted challenge with many critical factors. One of these factors is achieving stability and system safety in electrically noisy environments. Noise interference can be present on power lines, communication lines, internal interconnect, and even control/communication outputs from a wide range of external sources. Noise sources are common in industrial and automotive environments with high transient currents/voltages, high-powered communications, shock/vibrations, and other noise contributors.
Addressing Real-Time/Closed-Loop Control Embedded Device Challenges
Microchip offers several families of 8-bit MCUs and 16-bit MCUs/DSCs that are designed with real-time/closed-loop control applications in mind. These MCUs/DSCs come equipped with several functions and features that reduce processor burden, ensure reliability/system stability, mitigate noise interference, and enable operation in extreme environments. Moreover, Microchip provides an ecosystem of development tools, software libraries, reference designs, code examples, and other resources to ease development for the real-time/closed-loop control device for stringent industrial and automotive applications, including resources that aid with key certifications and standards compliance.
Reducing Processor Burden
There are several methods Microchip has used to reduce key MCU/DSC resource use for common real-time/closed-loop control applications, namely, Core-Independent Peripherals (CIPs), Intelligent Analog, Peripheral-to-Peripheral triggering, and dual-core 16-bit MCUs/DSCs when the resource requirements are high enough. These functions are available with several of Microchip’s 8-bit MCU and 16-bit MCU/DSC families, and all enable functions, operations, and actions that would typically require a central processor’s oversight (if not direct control).
CIPs for 8-bit MCUs and 16-bit MCUs/DSCs include peripherals such as Windowed Watch Dog Timers, Pulse Width Modulation, Configurable Logic Cells, High Endurance Flash Memory, Numerically Controlled Oscillators, Math Accelerators, Cryptographic Authentication Engines, and a wide variety of other control, communications, security, and actuator functions. Many of these peripherals (including timers, sensors, and security functions) can even trigger the action of other peripherals without the need for developing complex code or using central processor resources.
Moreover, many Microchip MCUs/DSCs for rugged embedded applications also include Intelligent Analog peripherals beyond just Analog-to-Digital converters (ADCs) and Digital-to-Analog converters (DACs). Some of these integrated peripherals are Operational Amplifiers, Digital Signal Modulators, Fixed Voltage References, Zero Cross Detect functions, Slope Compensations, and a variety of Comparators, which can be used to pre-processes inputs and reduce the processor burden of doing complex mathematics and conversions for control outputs. Overall, these MCU/DSC features can significantly reduce the processing power needed for a given application, opening-up resources for additional end-product features. Such substantial resource savings could also allow for the use of lower power and less expensive MCUs/DSCs.
Enhancing System Stability and Noise Immunity
Ensuring overall system stability includes a complex set of factors depending on what standards for compliance, operating conditions, and application-specific criteria are at play. Some of the most critical factors for many applications are memory stability, life, and error-free operation, along with noise immunity, robust communication, and Functional Safety operation. Microchip addresses these needs by offering MCUs and DSCs with high-endurance memory, error-correction code (ECC) memory, robust commu-nication protocols, excellent noise immunity, a high (5V) power rail, and Functional Safety compliance to several industry and automotive standards.
High-endurance and ECC memory provide reliability by minimizing the errors associated with memory decay and transcription errors. Microchip’s high-endurance flash memory allows for many more read/write cycles (i.e., hundreds of thousands) than typical Flash memory. For real-time/closed-loop control applications, where the memory may undergo hundreds of read/write cycles each day, the endurance of integrated or external memory can be the limiting factor of a device’s lifetime. For 16-bit MCUs/DSCs, integrated ECC memory is available, and it enables memory errors to be caught and corrected in real-time. This type of memory performs the corrections with very little latency and prevents memory errors from impacting a real-time control system.
Communication is another weak link with real-time/closed-loop control systems where reliable sensor information inputs and control signal outputs are necessary for appropriate and safe function. Robust communications protocols, such as CAN, CAN FD, and SENT, were designed for the automotive industry to transmit sensor information and pass control signals reliably. These protocols are now used in a wide range of industries for similar purposes, and many of Microchip’s real-time MCUs/DSCs include integrated interfaces capable of implementing these protocols.
Functional Safety is another standard derived from the automotive industry, and devices that are compliant with Functional Safety standards come equipped with features that force safe operation, even in the case of fault or other system failures. There are several standards and levels within those standards for Functional Safety, and compliance involves the hardware, software libraries, and code used to implement a control system. Hence, Microchip offers MCUs and DSCs with Functional Safety features, which include a range of reliability features such as system monitoring, redundancy, backup oscillators, GPIO pin ESD protection, and others.
The standard compliance facilitated by Microchip hardware and software libraries include IEC 60730 (levels A, B, and C), IEC 61508/SIL (Levels 1, 2, 3, and 4), as well as ISO 26262/ASIL (Levels A, B, C, D), which include ISO 26262-qualified compilers, Failure Modes Effects, and Diagnostic Analysis (FMEDA) report, device level safety manuals, diagnostics software, a MISRA plugin, and the third-party LDRA Tool Suite for functional safety compliance.
For example, Microchip’s 8-bit real-time/closed-loop control offerings include four families of MCUs: the PIC18F Q10, PIC16F1386, ATtiny1607 and ATmega4809, which are all equipped with integrated CIPs, Intelligent Analog, robust communication, and other features. These MCUs are well-suited for applications from industrial control and automotive, the Internet of Things (IoT), and consumer electronics. Several models within these families have added stability and noise immunity (5V rail) capabilities. Some of these models are also rated up to 150º C operation, which far exceeds the environmental requirements of most embedded MCUs and opens-up an expanse of possibilities for device placement within extreme systems.
There are many other 16- bit MCUs/DSCs that have Functional Safety features, such as the ones listed here, plus additional features that make them ideally suited for robust applications. These additional features include RAM BIST, Illegal Opcode detect, Windowed Watchdog Timer, PWM Fault Management, and other fault management/prevention features.
Along with capable hardware, capable software development tools and other resources are helpful in implementing real-time/closed-loop devices. Typically, these types of systems are supported by software that has a high learning curve and is very specific to the application and technology being used. With Microchip’s development resources, however, the software tools are widely compatible with Microchip MCUs, DSCs, and Microprocessors (MPUs). They are adequately featured to support virtually all embedded electronics applications and developers. For example, MPLAB® Code Configurator (MCC) is a graphical programming environment that can be used by experienced developers looking to save time, or it can be used by inexperienced developers hoping to reduce the learning curve of code development for real-time applications.
MCC is accessible freely through either MPLAB X Integrated Development Environment (IDE) or the cloud-based MPLAB Xpress IDE and is extensible with several key application-geared tools, namely motorBench® Development Suite and the Digital Power Design Suite [16, 17]. These suites come with development tools familiar to designers working on motor and power applications, and it makes determining and coding algorithms efficient and straightforward.
Moreover, Microchip provides a host of professionally developed code examples and reference designs for very specific applications. While a developer might typically need to comb through stacks of research documents, manuals, and books, or otherwise spend valuable development resources experimenting with several methods, a developer using Microchip’s reference designs and code examples is given easily integrated, working code along with the necessary background to rapidly start developing industrial-grade solutions.
Real Applications for Real-Time
Real-time, or closed-loop, control of electronics is essential for a variety of industrial applications, including heavy-duty motor control, real-time processing, robotics control and a variety of high-power applications. Given the environment, expense, and regulatory considerations involved, electronics that require real-time control must be designed with extensive care. The main challenges to realizing an industrial grade real-time control system include overburdening the CPU, overcoming software system complexity, enhancing system noise immunity, and ensuring system stability. Microchip offers several unique hardware and software solutions that aid real-time control designers in mitigating these challenges and enable the development of competitive industrial electronic products.