high-end of the European inverter and motor control markets have long been driven by the push to achieve the highest performance from a microcontroller and the fastest response to interrupts. These improvements in microcontroller performance have allowed for more intelligent and efficient motor control algorithms to be used. The high performance trend has been lead by the Renesas SuperH SH-2A core that offers up to 200MHz performance and a 6 cycle interrupt response time.
The SH-2A is now no longer reserved only for the high end of the European inverter market. With the introduction of the SH7243, high performance and fast interrupt response times are now available for application sectors.
The fast interrupt response times are made possible by arranging the core’s CPU registers in “banks”, with the 19 registers being mirrored 15 times. Using this technique, an interrupt subroutine can use a second set of registers leaving the current ones ready for use upon return from the interrupt. This means that the registers don’t need to be popped onto and back from the stack. The SH-2A core is an enhanced version of Renesas’ SH-2 core with a superscalar architecture. It has two execution units in the pipeline, allowing 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 SH7243 device offers a comprehensive MTU2 timer unit with six channels of 16-bit timers, support for up to 16 input capture/output compare functions, and a three-phase PWM capability for electrical motors. Additional motor control features are enabled by a quadrature encoder feedback capability and a special channel that can measure dead times at the power stage, thus enabling 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 quick shutdown of the motor. Also included is an MTU2S peripheral, this is simply a subset of the MTU2. This means that the SH7243 can drive two vector controlled industrial inverters simultaneously.
The IC includes two ADCs with four channels each, 12-bit resolution and 1.0us conversion time. Each ADC can be triggered by the MTU2 with an additional defined delay time to support algorithms such as single-shunt motor drive.
The device is complimented by, three UART channels, a watchdog timer, two channels of compare-match timers, and comes in a 100pin package (14x14mm 0.5mm pitch) that operates at 3.0V to 5.5V.
SH7243 options include 128kbytes flash versions with 8k bytes of RAM and 256kbytes flash versions with 12kbytesof RAM. The SH7243 is a smaller variant of the SH7280 series (SH7285 and SH7286) providing a 100% software compatible upgrade path to 1Mbytes of Flash, 32k of RAM and 176pin packages.