Square wave generation phase offset problems using PXI6602

Hi,

I am generating 2 signals to use for simunlating an Incremental AB encoder using a PXI6602.

The signals need to be square wave, 34.133Khz, offset by 90degrees which I am setting by dividing (1/frequency) by 4 and putting the result into the DAQmx Create Channel (CO-Pulse Generation-Frequency).vi initial delay node.

The resulting signals phase difference however does not consistantly measure 90degrees. At least 1 in 5 runs of the vi has a phase angle issue resulting in a failed test.

Can anyone suggest a stable fix for this.

Thanks,

David