Methods, apparatus, and systems for monitoring and measuring signal characteristics for signals received over a multi-wire, multi-phase interface are disclosed. Signals present on each line of a 3-line communication interface are sampled using auxiliary samplers having a programmable time delay to delay the sampled signal by a set time, as well as a programmable voltage offset. The auxiliary sampler outputs are compared with direct line samples of signals on each of the three lines to generate error signals. From this comparison, an array of error signal data occurring over a particular sampling period may be generated. In turn, waveform characteristics can be determined from the error signal data, such as an eye-pattern. Furthermore, skew measurement may further be effectuated using the auxiliary samplers but determining the time difference of when the error signals of the different wires cross a predetermined threshold.