Description
Yes the rx_freqlocked signal will assert in simulation if a constant ‘0’ or ‘1’ is applied to the rx_datain signal of Altera® transceiver devices.
In hardware, the rx_freqlocked signal is not asserted unless the clock recovered from the rx_datain port is within the parts per million (PPM) threshold relative to refclk, as defined in the device handbook.
To fix the problem, apply ‘Z’ to the rx_datain port in simulation which produces similar behaviour to silicon.