Solving an EMC/EMI problem occurred inside a complex programmable logic device

During the development of an electronic module using a complex programmable logic device (CPLD) and a micro-controller, we noticed an abnormal behavior of the CPLD manifested as an unexpected reset of a counter. We identified a synchronous perturbation and an asynchronous perturbation as being responsible for the disturbance, both of them being related to the change in the state of a large number of data lines. We devised and tested methods for eliminating both perturbations, the application of which helped in achieving the intended behavior of the device.