NI PXI-6652 The National Instruments PXI-6652 is a system timing and control module for PXI. The NI PXI-6652 features the ability to drive the PXI star trigger lines, import or export triggers to the PXI backplane, and generate a high-stability TCXO 10 MHz reference clock (1 ppm accuracy) for instrumentation. With these features, the PXI-6652 can be used to increase accuracy of instruments within a system, or to synchronize multiple PXI systems together.