Renesas Electronics Launches the SH7239 MCU for DSP Applications

The new MCU is the sister product to the world’s fastest embedded flash MCU which Renesas Electronics launched in February 2010. The SH7239 MCU includes many of the SH7216’s peripherals but has a reduced feature set, making it particularly suitable for the inverter control market. As the SH7239 MCU is a true MCU with a standard instruction set optimised for C code, software engineers no longer need to choose between a DSP for high performance signal processing and an MCU for ease of coding. The new MCU delivers the best of both worlds.

The new MCU is based on the powerful SH-2A core. The SH-2A core, an enhanced version of Renesas’ SH-2 core with a superscalar architecture, has two execution units in the pipeline. This allows two instructions to be processed concurrently and code can be executed up to twice as fast as the CPU clock. In addition, its Harvard-based architecture ensures that no bus conflicts occur between instruction fetch and data access. The SH-2A core also features an optional integrated double precision floating point unit (FPU). These features enable faster DSP functionality on the SuperH MCUs.

The core, which runs at up to 160MHz on the SH7239 MCU, is not the only fast part of the device. The SH7239 MCU is equipped with metal oxide nitride oxide silicon (MONOS) based flash memory, which allows execution at full speed with single cycle access to the flash. Some DSP-style architectures oblige system designers to copy their critical code into RAM in order to achieve faster execution time. This is unnecessary with the SuperH MCUs as MONOS flash is as fast as RAM.

For inverter control, the SH7239 MCU series offers a comprehensive timer unit (MTU2) with six channels of 16-bit timers, supporting up to 16 input capture/output compare functions, and a three-phase PWM capability for electrical motors. Additional motor control features include a quadrature encoder feedback capability and a special channel that can measure dead times at the power stage. This ensures both the shortest possible dead times for highest efficiency and safe, non-destructive operation of the power stage. The MTU2 also incorporates additional safety features with its port output enable (POE) pins that provide a faster and more deterministic response time to ensure safe, fast motor shutdown. Also included is an MTU2S peripheral, a subset of the MTU2. For high performance drives, the timer block can also be clocked with up to 100MHz.

There is a hardware trigger connection between the SH7239 MCU’s inverter timer unit and the three ADC blocks on the devices, which saves CPU loading and time. The 12 channels of ADC all feature 12-bit resolution and 1.0µs conversion time, and there are up to six independent sample and hold circuits in the device to support algorithms such as single-shunt motor drive.

Real time applications such as inverter control need a fast core as well as very fast response to external events, such as an emergency situation. The SH7239 MCU’s registers are arranged in 15 blocks or “banks”. This ensures that the registers do not need to be popped onto and back from the stack, providing a quicker return from the interrupt subroutine. As a result, the response time to an interrupt request (IRQ) is as fast as a simple branch instruction: 6 cycles.

The SH7239 MCU series features devices with 512k or 256k of Flash and 64k or 32kbytes of RAM. It comes in a 120-pin package (16x16mm 0.5mm pitch) and operates at both 5V +/- 10% and 3.3V +/- 10%.