Abstract: A digital control card based on digital signal processor was developed. Two Freescale DSP-56303 processors were utilized to achieve 3 channels proportional-integral-differential regulations. The card offers high flexibility for 100 MeV cyclotron RF system development. It was used as feedback controller in low level radio frequency control prototype, with the feedback gain parameters continuously adjustable. By using high precision analog to digital converter with 500 kHz sampling rate, a regulation bandwidth of 20 kHz was achieved.