- Industry 4.0 requires universal connectivity.
- Conventional electronics are too expensive and power-hungry to apply to all devices.
- Careful design minimizes burden to the processor, allowing one MCU to handle the primary application and networking tasks.
Enabling Cyber-Physical Systems for the Fourth Industrial Revolution
The buzz is building in the manufacturing industry about the fourth industrial revolution (Industry 4.0). The first industrial revolution of the 1780s was powered by steam engines, the second revolution of the 1870s saw advancements in food preservation and production/processing technologies. The 1970s saw the third industrial revolution, driven by automation that was in turn enabled by programmable logic controllers (PLCs) and advances in IT, particularly in automobile manufacturing plants.
Today, many believe that cyber-physical systems will drive the fourth industrial revolution. Cyber-physical systems aim to realize more intelligent production by linking physical equipment with cyber systems (computing science that involves the virtual world, such as cloud computing). In order to realize such architectures, cloud and other computer systems need to accumulate more information on real world equipment. In this article, we’ll take a closer look at the requirements presented by this goal and how the latest MCUs help achieve it.
Bringing together the real and the virtual
The concept of networking industrial equipment is no longer rare these days. Many OEMs and embedded designers are familiar with industrial Ethernet protocols like EtherCAT, MECHATROLINK, EtherNET/IP, and CC-Link that are used for connecting components and machines to each other and to the Internet. The issue is not embedding network functionality in some equipment. The issue is embedding network functionality in all equipment.
Presently, the components that are connected to the network in most plants represent only a handful that play a major role in the production process. Support components that surround this core equipment, like the multitudes of motors and universal inverters, operate outside of the network. Improvement in production efficiency and energy conservation across the entire plant using cloud systems can only be achieved by networking together every part of the physical system with the cyber system. In order to realize a true cyber-physical system, all equipment must have embedded network functionality.
So why is there a delay in the majority of factory equipment becoming network compatible, despite the availability of well-established networking technologies? Put simply, it’s harder than it sounds.
Presently, most non-networked industrial machines consist of key devices that include a power semiconductor for driving motors/inverters and a control-oriented MCU. On the other hand, most equipment that has already been made network compatible is equipped with a large-size system on chip (SoC) for the controlling system, along with a network-specific SoC. Thus, compared to non-network compatible apparatuses, such equipment consists of pretty sophisticated devices.
The easiest method for equipping such microcomputer control-based equipment is to add an ASIC dedicated to networking. It is not easy to add such processors to large devices due to issues of cost and size, however. Moreover, supplementing these devices is always accompanied by an increase in electricity consumption. Even if the increase is slight on a per-device basis, it will still result in a considerable burden in terms of electricity for an entire plant that uses a number of such machines. It is of no use to create an intelligent factory in the hope of conserving energy if consumption actually increases as a result of making equipment network compatible.
When supplementing new devices is not feasible, the only other solution is for the MCU to also perform networking functions. Today, in anticipation of such needs, vendors are developing microcomputers with Ethernet and network functionality into commercial products.
In theory, these network-compatible MCUs should be able to make all apparatuses network compatible. This has not been achieved, however, due to one major problem: the processing volume required to actualize network functions is large, while many MCUs have limited CPU and memory resources. As a result, MCUs frequently lack enough CPU or memory capacity to deliver network functionality while still performing their original functions of controlling motors or inverters. With careful design, however, ARM® Cortex® M-based MCUs can provide more than enough performance to serve both purposes.
Microcomputers for industrial 4.0
Developing an industrial-caliber MCU has to start with the right foundation, which means using an ARM Cortex M4 core. After that, every aspect of the design must focus on not just optimizing performance but on minimizing the burden on the processor. This can result in an MCU capable of supporting both the host application and networking capabilities.
To optimize performance, an MCU needs to operate at high speed and feature a significant amount of onboard flash memory and RAM. The Spansion S6E2CC series of MCUs, for example, feature a 2 MB of flash memory and 256 Kbytes of RAM, with a 200 MHz operating frequency. This gives it the resources to simultaneously support both high-precise motor/inverter processing and network processing.
Industrial-grade controllers need to provide multi-channel interfaces for bus protocols like Ethernet MAC and serial interfaces like USB, HDMI (particularly high-speed quad SPI), and UART/SPI/I2C. The Spansion S6E2CC series also supports the CAN-FD specification, which operates at speeds twice as fast as the traditional CAN standard.
Putting the peripherals on chip is another method for reducing the computational burden placed on the processor. Examples include timers, real-time clocks, timers, A/D converters, D/A converters, and more.
Timing functions can consume large amounts of processing resources. The Spansion S6E2CC series features a multi-function timer that supports an output compare unit (OCU) function and an A/D converter launch coordination function. The OCU function enables independent OCU settings on both the up-count and the down-count sides of the free-run timer (FRT), enabling the generation of waveforms with higher degrees of freedom, such as asymmetric waveforms (see figure 1).
The A/D converter launch coordination function downcounts the designated counter register set value after detecting a match between output comparison channels (see figure 2); thereafter, the offset launch that starts the A/D converter is enabled. Although such processing is used widely among motor/inverter controlling equipment, most previous MCUs have performed this step by counting the timer trigger on the CPU side. The Spansion S6E2CC series handles it using just the timer and without burdening the CPU.
The timer also achieves a PWM resolution of 5.00 ns and operates at a maximum speed of 200 MHz, the same speed as the CPU core. It can conduct an accelerated control that can fully leverage the high-speed switching ability of its next-generation gallium-nitride power device.
The MCU was designed to enhance the usability of 12-bit A/D converter (3-unit loaded) to deliver a high-speed sampling of 0.5 μs. A new window comparator function enables the user to set an upper/lower threshold and either a within-range or outside-range detection, as well as suppressing the CPU intervention from occuring with unnecessary data conversion (see figure 3). These changes also reduce the processing demands made on the CPU.
Another approach that minimizes processing demands is the use of a program cyclic redundancy check (PRGCRC) function to enhance the cyclic redundancy check (CRC). The PRGCRC can add custom polynomials without being limited to just CRC16 and CRC32. Speeding memory access also streamlines processing. The Spansion S6E2CC series, for example, includes a flash accelerator that allows the system to access memory with zero waiting time even during operation at 200 MHz. In addition, the peripheral bus primarily uses an AMBA high-performance bus (AHB) for the main bus, instead of a slower speed version, boosting access to 200 MHz (see figure 4).
The design even includes an SD interface in the external bus, in addition to making it compatible with the external SDRAM. An AHB independent of the designated controller was allocated to this SD interface, enabling data transfer without burdening the CPU, DMAC, or DSTC. This allows the MCU to maintain stable communication even when using a wireless module such as Wi-Fi that contains an SD interface.
As the volume of data on the network increases, the value of the network will rise with it. As a result, we will see a growing threat to the data on the network. In such an event, hackers will probably aim their attacks at the most vulnerable parts of the network, which is also likely to be most simple hardware component: MCU-enabled device.
In addition to being equipped with a hardware encrypting macro, the Spansion S6E2CC series has a function that can conduct the encryption processing indispensable for Ethernet compatibility such as AES and SHA-256. By using the aforementioned PRGCRC, the device accomplishes this without burdening the CPU. For data extraction risk via external memory-linked external bus, a library will be provided for transmitting bus data by scrambling it into a complex form. An additional function restricts the access to the flash memory by writing down a protection code in the security code field, prohibiting the reading and writing of data from an external drive.
Such security functions are durable enough to survive shock, vibration, contamination, and thermal swings presented by applications like automation and metering. An MCU thus equipped can be considered to have sufficient security for cyber-physical systems.
Fully realizing the promise of the fourth Industrial Revolution with its cyber physical systems requires that all devices be network compatible. To be practical, devices need a solution that is effective yet economical and power efficient. Technologies focused on minimizing the processing burden on the CPU can deliver an effective and secure MCU capable of connecting many previously stand-alone devices to the network while also supporting their primary operation. Soon, motors, sensors, thermostats, lighting, security, handheld meters, and more will become a part of the industrial Internet of Things.
For a complete discussion of the features of the Spansion S6E2C MCU Series, see the Product Spotlight in this issue titled “Next-Generation MCUs Enable the Industrial Internet of Things.”
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