A reference voltage value and a chip select (CS) signal timing delay provided to memory devices can be determined based on samples of the CS signal received by the memory devices. The CS signal can be provided to the memory devices with varying time delays and for various reference voltages. Various samples of the CS signal from the memory devices can indicate different times for rising and falling edges of the CS signal. A composite signal eye can be generated by the latest occurring rising edge and the earliest occurring falling edge of the CS signal. The reference voltage value and timing delay can be chosen based on the composite signal eye width that is the closest to a reference eye width.