How to make a FGEN_DAQmx_Scope synchronization?

[splitsecond]

I have a PXI-6224 DAQmx Card, a PXI-5122 Scope, a PXI-5401 Signal generator.(5401 is a  traditional device in MAX explorer.)

Now, 5401 generates a triangle signal. At the same time, I want 6224 & 5122 to make acquisitions. But how to ensure the three start at one time?

It seems that I should send a command(or a trigger) to 6224 and 5122 when 5401 starts generation. I use RTSI lines but it doesn't work.

Is it necessary to change sample clock or ref clock?

Thanks.