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

H8/Tiny SERIES

The H8/Tiny series has an internal 16-bit architecture that runs on 3 or 5 V. (An internal step-down unit is used when 5 V is supplied.) The general registers are increased to 32 bits wide (double word), which can be used as 16/16-bit registers, 8/16-bit registers, and 16/8-bit registers.

Additional functions were added to the basic H8 instruction set to make use of the 16-bit architecture. These include signed multiply and division, byte-to-word and word-to-double word sign extension, as well as software interrupt vectors (TRAPA). Multiple power-down modes, module standby, dual clocks, and fast oscillator stabilization times help reduce power consumption.

High-current output can drive LEDs without an external current driver. Peripherals for this device include a real-time clock, 8- and 16-bit timers, PWM, UARTs, I²C, and a 10-bit A/D converter. The H8/300H series is suitable for home appliances and electronics, small DC motor control, the mechanical control of office machines, and automotive control modules.

Dual synchronous/asynchronous UARTs and an I²C interface (master/ slave) give the ’3687 plenty of communication power. There are eight analog inputs to the 10-bit ADC. A conversion takes a maximum of 134 clock cycles. Single and continuous conversions are handled on a single- or multiple-channel basis. Power-on reset, a watchdog timer, and low-voltage detection circuitry help keep the MCU’s operation stable.

Two clock speeds are available 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. The Subactive mode has the CPU executing from the subclock.

The sleep instruction has six possible power-down modes. Sleep in High Speed mode halts the CPU while the on-chip peripherals function via the system clock. Subsleep mode halts 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 stops, 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 on-chip peripheral functions freeze. 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 programming mode for the MPU. In User mode, flash memory programming is handled under user program control by 1-, 8-, 16-, and 28-KB block erasures in addition to 128-byte block writes. Note that this is similar for the H8/300H and H8S series.

Programmer and Boot modes operate in the manner described in H8/300L SLP section of this article. To reiterate, the host indicates the length of the code (word) it wants programmed followed by the data. The MPU resets to USER after the data has been recognized.