32-bit MCUs provide 240MHz for real time operation

27th January 2015
Barney Scott

Doubling CPU operating frequency from 120 to 240MHz, Renesas has extended its RX Family of 32-bit MCUs with the RX71M Group. Developed for use in industrial equipment and described by Renesas as the ‘flagship’ product of the series, the group is available with up to 4MB of on-chip flash memory.

As system size and complexity increases, there exists a growing demand for greater adaptability and scalability from the on-chip flash memory MCUs commonly used in midrange industrial equipment. With the rise of dispersed, low-volume, high-mix development in preparation for the age of the IoT, the risk of leaked or duplicated core technologies (such as important algorithms) has also grown, necessitating development environments which offer security and confidentiality.

Because of their critical importance within systems, the MCUs used in industrial equipment need to operate in real time, but if access to flash memory is slower than the operating speed of the CPU itself, dedicated high-speed on-chip SRAM must be added, increasing BOM. 

Renesas developed the RX71M group with precisely these needs in mind, providing a 240MHz maximum operating frequency, which translates to performance of 4.4 CoreMark/MHz at 240MHz, among the best in the industry among flash MCUs. A total of 112 product versions are available, with package pin counts ranging from 100 to 177 pins and on-chip flash memory capacities from 2 to 4MB.

The RX71M maintains backward compatibility with earlier RX Family products in aspects such as peripheral functions, development tools, and pin assignments

Drivers are provided with support for Firmware Integration Technology (FIT), making porting software between RX MCUs even easier. Development time and cost can be reduced by up to 50% when porting programme code between RX products. This helps customers in their efforts to develop products based on a common platform.

To support the increasing diversity of communication standards accompanying the trend toward IoT, the RX71M expands the list of supported communication interfaces beyond the earlier CAN and SPI to include SD Host Interface, USB High Speed (built into the PHY), and dual-channel Ethernet with IEEE 1588 support. In response to the increased security risks accompanying the proliferation of communication standards, high-speed encryption functions (AES, DES, SHA, and RNG) are implemented in on-chip hardware, providing robust protection against leaks of important data and communication data.

Previous Renesas MCUs offered functionality to protect leaks of post-development code by preventing code stored in the on-chip flash memory from being read by external devices. The RX71M expands this coverage to the development stage with a trusted memory function that protects important algorithms from being leaked or copied without authorisation. The trusted memory function sets aside a special area of memory from which code cannot be read (copied) even by the MCU's internal modules, such as the on-chip flash memory. This function prevents core software technology from being disclosed, even when development takes place at overseas facilities or is undertaken jointly with other companies.

High-speed flash memory using the 40nm flash process and capable of operating at 120MHz, combined with the Advanced Fetch Unit (AFU) incorporating cache-based memory control, achieves performance equivalent to no-wait access when operating at 240MHz. Even if a cache miss occurs, the performance penalty is equivalent to only one cycle, so excellent real-time performance can be achieved even when using only the flash memory.

The available on-chip memory configurations extend up to 512KB of parity checkable user RAM, 32 KB of single error correction/double error detection ECC RAM and a maximum of 4MB of flash memory, the largest capacity available in this class of product. This makes it possible to do away with external high-speed SRAM. The RX71M allows customers to utilise the on-chip memory to the full, realising a reduction in BOM of as much as 45%.

For a quick development start, the RX71M MCU is supported by a robust development tool environment, including e2 studio, a powerful Eclipse-based IDE, as well as compilers, debuggers, code generation tools, and flash programmers. In addition, the RX71M device is supported by the IAR Embedded Workbench for Renesas RX compiler and IDE. RTOS and middleware is available from leading third-party companies such as Micrium, Segger, CMX, Express Logic, RoweBots, port GmbH and FreeRTOS.

Software examples and drivers are provided by Renesas, including FIT Drivers. FIT is a novel concept that emphasises the simplification of embedding peripheral function module drivers and improves the portability between RX MCUs. Software examples and FIT drivers can be downloaded from the Renesas website.

Samples of the RX71M MCUs are available, with mass production scheduled to begin in June 2015.

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