An IC with I/O configurable for coupling to different operating voltage environments

The core of an IC may be supplied with a reduced voltage by an internal voltage dropping circuit VDC, while the input and output circuits remain compatible with circuits supplied with an unreduced voltage. Alternatively, the IC may be supplied with reduced voltage, and the input can be configured to accept signals from circuits supplied with the reduced voltage (figure 4), or from circuits supplied with the unreduced voltage (figure 5). When the IC is supplied with reduced voltage, an output driver (figure 9a) may be protected against leakage currents by applying a boosted voltage, e.g. from a voltage pump, to some driver nodes. The same IC design may be used in different operating modes depending on the option selected by metal masks, by fuses, or by EEPROM, EPROM, or SRAM cells.