Hybrid Controller

Signal processing and computing power on a single device

Many automotive systems have shifted from being mechanically to electronically driven, with a typical car on the road today having 60 to 90 ECU processors. According to industry analysts, this figure is set to rise by 50% within the next 5 years. An increasing number of applications that have heretofore relied on microcontrollers (MCUs) now require the signal processing capabilities of digital signal processors (DSPs). As a result, they need the combined abilities of both types of chip. Typically, in such applications, a DSP will handle intense computational algorithms, while the MCU will handle interfaces, networking, control, etc. Combining both capabilities on a single IC, The Semiconductor Products division of Motorola Inc, Phoenix, AZ, has reduced system cost and power demands while improving efficiency and performance.

General-purpose control and digital signal processing have different requirements, and circuits optimized for each have evolved to different and specialized designs. DSPs are not optimized for control features and are difficult to program. MCUs are not efficient for signal processing tasks. Thus, control and signaling processing have been handled by two distinct device types. While DSPs are asked to perform mathematically complex tasks at the highest possible speed, and MCUs are required to communicate with and coordinate various subsystem activities, their programming architectures vary accordingly. MCUs are optimized for compilers and facilitate such easily programmed languages as C or C++; whereas, fixed-point architectures found in DSPs are not suited for high-level language compilers and require careful assembly language programming to optimize parallelism and performance.

Merely adding on control functions to an existing DSP architecture would impair performance and require excessive amounts of additional memory. Integrating DSP and controller code onto the same chip would require excessive use of silicon. The solution Motorola engineers decided upon for their hybrid controller was to combine an optimal mix of instructions, based on a study of which DSP and MCU instructions are most frequently used and beneficial. By supporting those instructions that have the greatest impact and avoiding less frequently used instructions, designers streamlined the architecture. The hybrid excels at traditional microcontroller functions, such as bit field operations, branches and indexed address, as well as signaling process tasks, such as multiply/accumulate (MAC), parallel data moves and filtering, all with minimal silicon usage and low chip cost.

The 56F8300 series combines signal processing, fast flash and fast clock speed in 16-bit devices, suiting it for use in applications previously consigned to 32-bit MCUs. The series executes code from its third-generation flash up to 60 million instructions per second (MIPS), without using acceleration technology. Enhanced I/O capability increases flexibility, with 76 general purpose I/O, 32 to 256 kB on-chip flash memory and support for 32 MB off-chip scalability. Future models in the series are planned for up to 512 kB program flash. 

The series is designed to withstand harsh environmental factors, such as temperatures between -40° to 125°C, heavy surrounding debris, and abrasive movements like vibration and shock. Safety-critical functions include an integrated sensor for component temperature monitoring, multiple fault conditions for system flexibility, built-in write protection registers for critical functions, and on-chip clock synthesis that allows shutdown for system damage protection. An integrated FlexCAN module offers CAN capability and handles all networking communication. A flash security feature prevents unauthorized reproduction of proprietary code. Power-saving features are also included. 

System development is further enhanced by the MC56F8300DSK demonstration board, from Metrowerks, based in Austin, TX. The board includes the CodeWarrior development studio for 56800 and demonstration code to get system designers up to speed quickly. The Processor Expert auto-code generator is designed to reduce development time, improve code quality and reduce time to market. It eases the process of integrating code to different MCUs within Motorola’s controller lines. 

Applications for these hybrid controllers include drive-by-wire functions such as power-assisted steering, torque, braking and traction control, and occupant detection. The devices can apply to non-automotive applications such as electronic currency recognition for vending machines, continual power supply for industrial grade motors, and even medical applications, such as bone growth stimulation.

—SG

Metrowerks,
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