DS90UB948-Q1: What does the LOCK output shows

Part Number: DS90UB948-Q1

I have configured the DS90UB948-Q1 deserialiser like in the application note: (I configured the auto-scrolling configuration) http://www.ti.com/lit/an/snla132d/snla132d.pdf. I am using the internal pattern generator function. In this case, what does the LOCK output shows in this case ? LOCK = 1: PLL acquired lock to the reference clock input