Choosing the right microcontroller unit (MCU) is a crucial decision when designing any embedded system. For industrial automation applications, factors like performance, peripherals, power consumption, development tools and cost become especially important. The Cortex-M0+ series of MCUs from ARM offer an attractive option for such applications due to their combination of low cost, low power and good performance.
What is Cortex-M0+?
The Cortex-M0+ is a 32-bit ARM processor optimized for low-cost and low-power embedded applications. It is the smallest and most energy-efficient ARM processor available, making it well-suited for industrial automation applications where cost and power consumption are major constraints.
Compared to the more powerful Cortex-M3 and Cortex-M4, the M0+ has a reduced pipeline length and does not include a memory protection unit or floating point unit. This simplification reduces silicon area and power consumption. However, it still includes key features like the NVIC for interrupt handling, SysTick timer and debug capabilities.
Benefits of Cortex-M0+ for Industrial Automation
Here are some of the major advantages of using a Cortex-M0+ MCU for industrial automation designs:
- Low Cost – The simplified design of the M0+ allows it to be manufactured very cost effectively. MCUs based on it can sell for under $1 in volume.
- Low Power – With dynamic power consumption under 200 μA/MHz, the M0+ can help minimize energy usage.
- Good Performance – It delivers 1.25 DMIPS/MHz, enough for many automation tasks like motor control, sensor monitoring and communication.
- Small Footprint – The Cortex-M0+ core occupies less than 12,500 gates, leaving more space for peripherals.
- ARM Ecosystem – Software, tools and support from the extensive ARM ecosystem can help accelerate development.
This combination of attributes makes the Cortex-M0+ stand out for cost-sensitive and power-constrained industrial applications.
Selecting a Cortex-M0+ MCU
The Cortex-M0+ core is licensed by ARM to many different silicon vendors who integrate it into their own system-on-chip (SoC) designs along with peripherals, memory and other custom blocks. As such, there are many Cortex-M0+ based microcontrollers to choose from for an automation project. Here are some key factors to consider during selection:
Peripherals
The peripherals integrated on the MCU will determine how much external circuitry is required. Industrial automation applications typically need interfaces like:
- ADCs to read sensors
- PWM for motor control
- Timers for time-critical tasks
- Communication like CAN, RS-485, Ethernet for connectivity
- Digital IO lines to drive relays and read switch states
Having many of these on-chip reduces BOM cost and board space requirements. Therefore, carefully evaluate the peripherals on each MCU and select one that best matches the application’s interface needs.
Memory
Most Cortex-M0+ MCUs have up to 256 KB of flash memory for code/data storage and up to 32 KB of SRAM for data variables. For simple automation tasks like reading some sensors and controlling a few motors, this may be sufficient. For more complex tasks involving lots of sensor data or variables, an MCU with maximum memory may be preferable to avoid running out of space.
Packaging
MCUs come in through-hole, QFN, QFP, BGA and other packaging options. For industrial environments, through-hole packages provide more robustness against vibrations/shocks compared to surface-mount options. However, they take up more space on the PCB.
Development Tools
The availability of low-cost development boards, debuggers, compilers and IDEs for the MCU can help accelerate prototyping and development. Most vendors provide evaluation kits for their chips. Ensure there is a robust development ecosystem around the MCU you select.
Operating Temperature Range
Industrial automation systems often must operate reliably across a wide temperature range like -40°C to 85°C ambient. Not all MCUs support this, so choose one with an operating range suited for the target environment.
Certifications
For applications requiring functional safety or compliance with standards like IEC 60730, it is important to select an MCU with the appropriate safety certifications like IEC 61508. This ensures the chip meets requirements like fault detection, fail-safe modes, documentation, etc.
Reliability Testing
The MCU must deliver stable, dependable operation across its lifetime in the field. Review reliability test results like HTOL, temp cycling, EMC/ESD to ensure the MCU can survive industrial environments and deliver a long mean time between failures (MTBF).
Vendor Reputation and Support
The vendor’s track record with quality, security and functional safety is important. Also consider their longevity in the market, availability of long-term chip supply and local support services. This minimizes supply chain risks and helps accelerate troubleshooting.
Example Cortex-M0+ MCUs
Here are some example Cortex-M0+ based MCUs suitable for industrial automation applications:
- STM32L0xx – Ultra low power series from STMicroelectronics with 80 DMIPS performance, memoir encryption for IP protection and hardware safety features.
- SAM D10/D11 – Microchip MCU with integrated USB and 12-bit ADC, targeted at motor control, power conversion and general automation.
- EFM32 Pearl Gecko – From Silicon Labs, combines low power consumption with high performance and advanced peripherals.
- MSP430FR2xx – Texas Instruments MCU with Ferroelectric RAM for ultra low leakage current and fast wake-up from sleep.
- NXP LPC800 – Scalable family with good mix of power, performance and cost-effectiveness.
Development Tools
Here are some commonly used development tools for Cortex-M0+ MCUs:
- IDEs – Software platforms like Keil MDK, IAR EWARM and mbed provide editors, compilers, debuggers and other functionality.
- Discovery/Nucleo Boards – Low-cost development boards with built-in debug from vendors like STMicroelectronics and NXP.
- JTAG Debuggers – External debug probes like Segger J-Link and ST-LINK allow flashing, debugging and tracing via JTAG/SWD interface.
- Emulators – Advanced tools like ULINKpro or MicroXplorer provide real-time emulation and debugging via high-speed trace ports.
- RTOS – Real-time operating systems like FreeRTOS for task management and scheduling.
- Firmware Libraries – Vendor-provided firmware libraries ease developing interfaces like USB, Ethernet, file systems, etc.
This robust toolchain helps boost developer productivity on Cortex-M0+ projects.
Conclusion
The Cortex-M0+ offers an optimal combination of low cost, low power and good performance for industrial automation applications. When selecting an MCU, carefully evaluate peripherals, memory, packaging, development tools, certifications and other aspects to find the best fit. Leading vendors provide a diverse range of M0+ based MCUs tailored for different industrial use cases. With the right MCU choice and development tools, engineers can develop efficient, reliable and cost-effective automation systems.
