Patent ID: 8111784

Claim:
A method of determining at least part of an eye of a serial data signal that includes a plurality of successive repetitions of a multi-bit data pattern comprising: controlling phase of a clock signal to establish an eye slice location for use as a location at which voltage of each bit in the data pattern can be compared to a controllably variable reference signal voltage; causing the reference signal to have a base line voltage; comparing the voltage of the serial data signal to the base line reference signal voltage at the eye slice location in each bit in the data pattern to produce a reference value for each of the bits; and gradually increasing the reference signal voltage and for each such increase, again comparing the voltage of the serial data signal to the reference signal voltage at the eye slice location in each bit in the data pattern until for some bit a result of the again comparing is different than the reference value for that bit; and storing as an upper value of the eye at the eye slice location information indicative of the reference signal voltage when the result of the again comparing was different than the reference value for that bit.