FlexRIO sampling points slip between runnings

[zyb1003]

Hi guys,

I got NI 7972 FlexRIO card running under 100MHz data clock. The data generation and acquisition is in the same SCTL. 

Now I am doing IQ sampling on a 25MHz signal. Here is my problem: between each running of FlexRIO, the first sampling point slips and it results that my phase calculation arctan(I/Q) randomly selected between 4 values. Any idea to solve this? 

[zyb1003]

More to add, I am using PXI backplane as ref clock in. The 25MHz signal is also generated from FlexRIO. 

[Terry_ALE]

Which FlexRIO Adapter Module (FAM) is connected to the 7972?

[zyb1003]

It is Ni 5783

[Terry_ALE]

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@zyb1003 wrote:

It is Ni 5783

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Which clock is driving the SCTL?