Bit 0 indicates a power fault condition. Voltages on each fused
section of both the SSP CPU and Control boards are monitored and a power
fail signal is asserted if any voltage falls below tolerance. Indication is
made by LEDs fitted to each board, optionally by a front-panel LED, and by
setting bit 0. If a power fault exists on the CPU board the FASTBUS slave
interface will still function. However a fault on the Control board will
probably render the slave interface inoperative.