plotting eye diagram in matlab

I have an ideal 16 Gbps PRBS 7 NRZ signal which I have generated in Matlab using stairs function. I have the x and y columns having time and actual signal values. I have a NRZ_data variable having x values in 1st column and y values in 2nd column. By using eyediagram(NRZ_data,127), I am expecting an eye diagram in only one unit interval. But, I am not getting a proper eyediagram. Please can someone tell me how can I get a proper eye diagram of 16 Gbps PRBS 7 NRZ signal?

Best Regards, Dsagar