Issue 157 August 2003
Spotlight on Renesas H8 Family
Hitachi and Mitsubishi Market MCUs for Embedded Systems

H8/300L SLP SERIES

The H8/300L super low-power series runs on reduced voltage (some devices down to 1.8 V). Most are in the 3- to 5-V range. Multiple power-down modes, module standby, dual clocks, and fast oscillator stabilization times help reduce power consumption to a minimum. On-chip LCD drivers and an internal voltage booster simplify external LCD interfacing. High-current output can drive LEDs without an external current driver.

The 300L SLP includes several peripherals: 8- and 16-bit multipurpose timers, an asynchronous event counter, 10-bit PWM, a serial communications interface, a watchdog timer, and a 10-bit A/D converter. The low-power consumption and LCD drive capability make the device ideal for battery-powered hand-held applications that require a customized or standard LCD.

If you require long battery life, you can reduce current consumption by placing the micro in Sleep mode. Power is a function of the amount of time the micro spends in Operating mode between sleep cycles. In many applications, the oscillator stabilization period is longer than the actual time of code execution before going back to sleep; therefore, it’s a major factor in current consumption. The oscillator stabilization time for the SLP series is on the order of microseconds as opposed to milliseconds, so it can save precious power at each wakeup.

There are three clock speeds for program execution. In Active High Speed mode, the CPU and all of the on-chip peripheral functions are enabled, and execution occurs via the system clock. In Active Medium Speed mode, the CPU and all of the on-chip peripheral functions are enabled, and execution proceeds via a divided system clock. Finally, the CPU executes from the subclock in Subactive mode.

The sleep instruction has seven possible power-down modes. Sleep in High Speed mode halts the CPU while the on-chip peripherals function via the system clock. Sleep in Medium Speed mode stops the CPU while the on-chip peripherals functions via the divided system clock frequency.

Subsleep mode freezes the CPU while the time base function of TimerA, TimerC, TimerF, TimerG, SCI, AEC, and the LCD controller/driver operate on the subclock. In Watch mode, the CPU halts, and the time base function of TimerA, TimerF, AEC, and the LCD controller/driver operate on the subclock.

In Standby mode the CPU and all of the on-chip peripheral functions are paused. Module Standby mode allows individual on-chip peripheral functions specified by software to enter Standby mode.

A number of I/O bits are responsible for setting the MPU’s programming mode. In User mode, flash memory programming is handled via user program control by 1- and 28-KB erasures and 128-byte block writes. In Programmer mode, the MPU is programmed using a PROM programmer.

In Boot mode, boot code is executed that uses the UART (TX/RX) to communicate with an external host program. The boot code auto bauds on incoming data (H’00’), and acknowledges and erases the flash memory. (Note that the data rate is automatically determined by analyzing the datastream via the auto baud process.) The host indicates the length of the code (word) it wants programmed followed by the data. After all of the data has been acknowledged, the MPU can reset to User mode for user program execution.