Digital low level RF systems for Fermilab Main Ring and Tevatron

New low level RF systems are successfully operating the Fermilab Main Ring and Tevatron. The upgrade replaces aging CAMAC and NIM components, and increases system accuracy, reliability, and flexibility. VXI LLRF systems feature a custom three channel direct digital synthesizer (DDS) module capable of independent or ganged operation in both frequency and phase modulation. Frequency and phase values are computed at 100 kHz by the module's Analog Devices ADSP21062 (SHARC) digital signal processor. The DSP concurrently handles feedforward, feedback, and beam manipulations. Higher level state machines and the control system interface are handled at the crate level using the VxWorks operating system. This paper discusses the hardware, software, and operational aspects of these LLRF systems.