Superconducting cavities are widely used as accelerating structure, especially for FEL experiments. Even in a single project, the cavities are used in many different systems. Therefore multiple applications require not only different cavity parameters (such as loaded Q, bandwidth, resonance frequency) but also specific modes of operation (pulsed, CW). The paper presents the implementation of multipurpose LLRF field controller suitable for large span of such systems. The controller is implemented for reconfigurable FPGA chips and can be used with various hardware platforms. Implementation issues are described together with operation experience in such facilities as FLASH.