Publication date: 20 September 2011
From consumer electronics and office equipment to industrial systems and automotive designs, today’s increasingly ‘connected’ world challenges embedded system developers to deliver applications with a wide variety of potential interface and connectivity options. At the same time demands to keep cost, space, power consumption and design time to a minimum puts pressure on developers to seek out solutions that optimise performance and efficiency, reduce component count and simplify design, prototyping and testing.
Among industrial equipment, an RS-232/485 port has been the staple external interconnect for essential maintenance, but many machines also now boast a USB port. This simplifies connection of peripheral devices or up/downloading of data, allowing a wider variety of users to interact with the machine effectively to fulfil their responsibilities. Moreover, using Ethernet to connect complex industrial equipment such as printers or CNC machines, or telecom switches, to an enterprise LAN is opening many new opportunities to collect detailed performance or usage data and to implement low-cost remote maintenance.
Enhanced connectivity is also being driven into automotive applications. With growth in demands for extra comfort and safety features, and Driver Assistance Systems (DAS), control networks using standards such as CAN and LIN are becoming more prevalent, even in lower range vehicles. These are already widely used for connecting subsystems such as engine management units and mechatronic modules, and deliver advantages such as increased modularity, weight/cost savings, and easier collection of diagnostic information. At the same time the robust nature of the CAN bus is seeing this standard continue its migration from the automotive arena to many industrial applications.
Networks such as CAN and LIN are increasingly sharing space with consumer connections such as USB and DVI as today’s car buyers expect to plug in devices such as mobiles, game terminals and DVD players for entertainment and information on the move. Automotive Ethernet is another interesting development currently gaining traction. This could enable a further step forward by connecting the vehicle to a home network to synchronise files such as music, video or phonebook contacts; as electric cars enter the mainstream, there could be more reasons to plug in than simply to charge the battery.
The embedded design community must respond to the increasing demands for convenient, seamless connectivity coming from these and other sectors. Embedded microcontrollers, for example, must now support many combinations of connections if they are to help developers simplify designs, reduce code size, trim board dimensions and speed up time to market.
To achieve this, processing capabilities must increase to handle multiple I/O channels and protocol standards. Also, with increasing ad hoc connectivity, enhanced security such as authentication and encryption is required. At the same time, cost pressure is ever present.
The ARM® Cortex™-M3 processor emerged to satisfy general demands within the embedded space for improved performance, efficiency and ease of use. With ARM’s experience in mobile applications, it is highly energy efficient and has a high-density instruction set that allows smaller code leading to reduced silicon costs. The 32-bit Cortex-M architecture delivers more performance per MHz than competing embedded processors, which allows developers to implement richer features at lower power consumption.
For applications requiring high-speed connectivity, or where multiple interfaces supporting concurrent operation are needed, the Cortex-M3 is able to execute the required tasks without significant increases in operating frequency and can allow greater use of power-saving modes; most 8-bit or 16-bit processors typically require a higher clock speed or longer active duty cycle to complete the same operations.
Another strength of the ARM Cortex-M3 is that this has become a de facto industry standard for high-performance embedded applications. Among the leading Cortex-M3 licensees, Toshiba has used this advanced core in its TMPM36x family of microcontrollers; enabling these MCUs to integrate peripheral features optimised for applications in sectors such as industrial, consumer and automotive. As such, the majority of family members provide plentiful I/O interfaces supporting standards that are widely used in these sectors. Figure 1 shows the connectivity roadmap for this family of devices.
A more specific example is the TMPM366, which targets applications such as industrial control and office automation. This MCU provides a combination of single-channel USB-Device controller, a 2-channel serial bus interface that can be configured for S or synchronous-mode communication, a 3-channel synchronous serial interface (SSP), a 2-channel general-purpose serial interface supporting UART or synchronous modes, and a single-channel UART supporting UART and IrDA 1.0. These interfaces are implemented alongside monitoring and control peripherals such as a 12-channel, 12-bit ADC capable of 1µs conversion time, a 16-bit timer and a watchdog timer.
For embedded applications such as office equipment and industrial control systems where minimum power consumption and component count and high levels of connectivity are key design criteria Toshiba has used the ARM Cortex-M3 to develop the TMPM361 and TMPM363. Both have a 5-channel general-purpose Serial I/O (SIO) and 3-channel Serial Bus Interface (SBI).
All variants have a synchronous serial bus interface (SSP) that supports SPI, SSI and Microwire formats. Peripherals partnering these interfaces include a 10-bit ADC, a 16-bit timer and a watchdog timer. In addition, a Consumer Electronics Control (CEC) unit and a remote control signal pre-processor (RMC) speed up completion of designs featuring remote control functionality.
Another variant, shown in figure 3, implements three key major connectivity standards for embedded applications – USB Device/Host, CAN2.0B and 10/100 Ethernet - together in one device.
Standard peripherals also on-chip include a 12-bit ADC, 10-bit DAC, 16-bit timers and support for multiple interrupt sources. With the advanced performance of the Cortex-M3, developers can also host features such as motor controls, user-interface control and display interfacing on the MCU, in equipment as diverse as domestic appliances, modules for smart buildings, patient monitors, retail technology and industrial automation. Furthermore, the incorporation of a Multi Purpose Timer that combines three-phase PWM control with an ADC trigger and a protection circuit is particularly relevant in motor control applications.
Utilizing this advanced technology, Toshiba plans to introduce a series of fully qualified automotive MCUs optimised for applications that require in-vehicle audio playback from MP3 players and external USB devices or SD cards. These will combine up to 1Mbyte of Toshiba NANO Flash™ memory, as well as peripheral features such as a 10-bit ADC and timers, with rich connectivity including USB 2.0, CAN functionality, a serial bus interface offering either I2C or synchronous operation, and general-purpose serial I/O (SIO).
Among these technologies will be the TMPM327C3D, based on an ARM Cortex-M3 core operating at frequencies up to 144MHz. As well as built--in connectivity including USB 2.0 High Speed Host Control, SDHC control, I2C and I2S interfaces, this device can also manage visual I/O
applications such as the display of images from a vehicle’s rear view camera (figure 4). As the diagram shows, in this case an integrated graphics engine, video input and digital RGB output further reduce external component count, while a special bus structure reduces CPU load during display and audio control.
