Mo & Terry Smedley


H8 Cascade Interrupt Expander


This board cascades eight additional interrupt channels onto one of the native interrupts of the H8.  The cascaded interrupts are disabled at hardware reset or power on, and remain disabled until explicitly (and individually) enabled via software.  This permits development of or experimentation with interrupt-driven hardware without being concerned with changes to firmware to handle power-on initialization of the interrupting device.  The circuit is based on the interrupt circuitry found in the Heathkit HERO-I robot.  This standalone circuit card uses LED bar graphs to show interrupt register status which assists with debugging.  The basic interrupt circuitry, minus the LEDs, is also found on the System Support II card for systems that are "less experimental".