AD9689 MNTO always low

I use AD9689 MNTO pin to synchronize multiple ADCs. I configure GPIO A1 as MNTO for the master ADC

and GPIO A1 as SNTI for the slave ADCs. Following Table47 to setup register 0x0042=0xF8 for master

and 0x0042=0xF9 for the slaves. I never see MNTO pin high with SYSREF pulses triggered.

Is there anything i miss and please advise.