One method design teams can use to reduce the time between project approval and production (and subsequent cost-effective mass manufacturing) is to minimize the learning curve associated with microcontroller technologies and their respective development tools. At the same time, selecting microcontrollers with application-specific features and functions can shorten the time spent implementing those functions, allowing designers to focus on their core design skills, which will give the final product a maximum competitive advantage.
These factors fuel the ever-expanding range of microcontrollers that combine industry-standard processing cores with integrated application-specific functions. Offering products with the same underlying core architecture makes it easier for developers to meet new design requirements by leveraging skills and knowledge gained from previous projects and exchanging know-how among different teams involved in the project. Furthermore, selecting microcontrollers that fulfill key application functions not only shortens the time required for circuit design and software programming but also reduces the number of components, which in turn lowers bill of materials costs, saves board space, and simplifies final manufacturing.
ARM Cortex™-M3 Microcontrollers
Among the most common industry-standard cores is the ARM Cortex™-M3 RISC, which has been optimized for deterministic, real-time applications. It offers high performance levels while addressing the challenges of reducing dynamic and static power consumption. This core enables microcontrollers to deliver 32-bit performance at a cost previously associated with 16-bit technologies. It executes the Thumb®-2 instruction set for optimal performance and code size—including hardware division, simple cycle multiplication, and bit field manipulation—and can be configured with up to 240 system interrupts, each with individual priorities and dynamic reprioritization.
Once an ARM Cortex-M3 core has been selected for the design, developers must choose the most appropriate device from a range that grows daily. Toshiba Electronics, for example, now offers five different families of ARM Cortex-M3 microcontrollers, each designed to meet the needs of a specific type of application. The 16 devices belonging to these families allow designers to choose ideal solutions for any purpose, from managing battery-powered portable equipment to controlling variable-speed motors, which are increasingly used in pumps, fans, and household appliances.
High-Capacity Flash:
One example is the Toshiba TMPM360, the first 32-bit microcontroller to combine the ARM Cortex-M3 core with 2 MB of onboard flash memory (Figure 1). This device was specifically developed for industrial and consumer digital applications that require a minimal number of components to deliver high performance, low-power operation, high-capacity data storage, and numerous serial interfaces.
Like other microcontrollers in the ARM-Cortex family, the TMPM360 uses Toshiba's NANO FLASH™ memory for its on-chip ROM. This technology combines the best attributes of NAND flash cells with the advantages of NOR flash memory peripheral circuitry. The result is a high-density onboard memory that operates with ultra-low power consumption and provides short program and erase times, as well as fast random access.
As shown in Figure 1, in addition to the core, which operates at frequencies up to 64 MHz, and the ROM, the TMPM360 also features 128 KB of onboard RAM and extensive serial connectivity with 16 general-purpose input/output channels, configurable for synchronous mode or up to 12 UARTs; a 5-channel serial bus interface (SBI), operating in I2C or synchronous mode; and a synchronous serial bus interface (SSP), supporting SPI, SSI, and Microwire formats. Furthermore, thanks to a consumer electronics control (CEC) unit and a remote control signal preprocessor (RMC), the device simplifies the design of applications with remote control functions. Other on-chip peripherals include a high-speed 10-bit analog-to-digital converter (ADC), a real-time clock (RTC), a watchdog timer (WDT), and a 16-bit, 16-channel timer.
Low Power Options
For many designers, low power consumption is the most important criterion in their work. For this reason, products such as the ultra-low power TMPM395FWXBG (Figure 2) have been developed.
Operating at voltages as low as 1.7 V and supplied in a 6 mm x 6 mm BGA package, the TMPM395FWXBG is ideal for a wide range of applications, from portable and battery-powered devices to household appliances and consumer electronics. The high-efficiency ARM core, operating at frequencies up to 20 MHz, and an optimized design ensure minimal power consumption during operation. In addition, several standby modes reduce current to levels as low as 1 µA (RTC mode) when the processor is idle.
Like the TMPM360, this microcontroller also incorporates CEC and RMC functions. Furthermore, an oscillation frequency detector (OFD) provides hardware monitoring of the CPU clock (Figure 3) and automatically detects abnormal clock operation without requiring complex software programs, making it considerably easier to meet the requirements of the IEC60730 (Class B) safety standard. This is an important aspect in many appliance designs.
The TMPM395FWXBG comes with 128 KB of flash memory and 8 KB of RAM and integrates a 10-bit, 12-channel ADC, an RTC, a 16-bit, 10-channel timer, and a WDT. It also incorporates a voltage detector and a high-speed 10 MHz internal oscillator. Connectivity includes a general-purpose, 3-channel serial interface, configurable for either UART or synchronous mode, and a 2-channel serial bus interface, selectable between I2C or synchronous mode. It also features a 4-channel SSP interface, offering a 3V tolerance SPI mode. To help designers optimize power efficiency, the TMPM395FWXBG includes four sleep modes – 'idle', 'slow', 'sleep', and 'back-up stop' – and three sub-clock (32.768 kHz) operating modes – 'slow', 'sleep', and 'RTC'. In RTC mode, current consumption is as low as 1 µA.
Motor Control:
One application area that has gained increasing importance in the development of embedded solutions is motor control. OEMs have faced increasingly stringent commercial and legislative imperatives to improve the efficiency and functionality of applications ranging from industrial pumps and fans to washing machines and dishwashers. This has driven the design of variable-speed motors, based on brushless DC (BLDC) three-phase motors. Variable-speed motors require far more complex motor regulation and control techniques than conventional constant-speed motors, especially if they are designed for sensorless operation. For this reason, designers are seeking microcontroller solutions that will allow them to meet these complex challenges without having to dedicate more time or resources than absolutely necessary.
Vector control, also known as Field-Oriented Control (FOC), is generally preferred in brushless motor systems. This complex control technique manipulates motor currents and voltages to maintain a constant stator field in quadrature with the rotor field, which has resulted in significant overhead costs for software development and implementation. However, dedicated microcontrollers that integrate vector control into the hardware have recently become available. These microcontrollers not only minimize the need for software programming and code storage but can also improve overall motor control performance.
One example is Toshiba's TMPM370 series, based on the ARM Cortex-M3 core operating at 80 MHz. This simple 100-pin integrated circuit integrates Toshiba's proprietary PMD3+ programmable motor control system and a vector motor (VE), as shown in Figure 4.
The TMPM370 series is ideal for compressors, fans, and other applications requiring BLDC motor control with or without sensors, as well as for appliance designs based on three-phase induction motor control. Its simple 5V operation, combined with a built-in OFD, also makes it attractive to appliance designers. The PMD and VE functions handle PWM waveform generation, speed control, and position estimation, freeing up the ARM core to manage other elements of embedded solutions. Integrated features such as a 12-bit ADC, comparator, amplifier, and encoder, along with a wide range of interfaces, reduce the need for additional components.
Development Support
When selecting the most appropriate microcontroller for a given application, it is also important to consider the availability of development tools and additional support materials. All of the microcontrollers described above have their own specific starter kits, designed to enable engineers to quickly begin production development. Depending on the target processor, these kits include evaluation boards; application-specific hardware (in the case of the TMPM370, for example, motor and motor control); detailed application notes; software development tools, such as in-circuit emulators (ICEs) and debuggers; and comprehensive documentation, including application notes, reference designs, and bill of materials information.
The author
Roland Gehrmann heads the Consumer and Industrial IC Marketing department at Toshiba Electronics Europe.
