First make sure the volts per division on channel 1 and 2 are the same, that the probes on both channels are set to 1:1, and that both channels are DC coupled. Then press the "Horiz" button at the top of the scope in the "Horizontal" section. Turn the knob in the middle on the left with the circular arrow icon to "XY" which will be displayed on the screen. Press the knob in to select XY.
Make your 1024-point complex input array X[N] an external (global) array. This causes X to be stored in a fixed location in memory. When you make your spectrum analyzer, your interrupt service routine declared with the keyword "interrupt" can have no arguments, so you must pass arrays to it as external arrays.
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