This paper proposes a hardware modification to a standard Digital Signal Processor (DSP) that enables it to digitally control multiple DC-DC converters with non-integer switching frequency ratios. The modified DSP overcomes the drawbacks of conventional DSPs, which are attributable to large variations in the delay from when the Analog to Digital Converter (ADC) samples the output voltage to when the duty cycle is updated. By incorporating modified interrupt control logic in the DSP, the effects of a variable delay are minimized by significantly reducing the worst case sampling to duty-cycle-updating delay. Applying this DSP to a multi-rail power supply system provides the designer with the flexibility to choose arbitrary switching frequencies for individual power converters, thereby allowing optimization of the efficiency and performance of the individual converters.