NI PXI-6683H is a timing and synchronization module for PXI and PXI Express test systems. NI identifies this model as a “TCXO, GPS, IRIG-B, IEEE 1588 PXI Synchronization Module,” positioning it as a primary synchronization device rather than an accessory. The module uses an onboard TCXO and the NI product page specifies 1 ppm onboard clock accuracy. Official protocol support includes GPS, IRIG-B, IEEE 1588, and PPS, with IEEE 802.1AS listed on the current NI page for Linux only. https://www.ni.com/en/shop/hardware/system-timing/model-pxi-6683h https://download.ni.com/support/manuals/373656c.pdf
The PXI-6683H is the hybrid-slot-oriented variant within the PXI-6683 family. NI states that it is designed for installation in a hybrid slot in a PXI Express system, and the official product flyer lists slot compatibility as PXI or PXIe Hybrid Peripheral Slot. The NI product page lists the bus connector as PXI Hybrid. Front-panel elements documented for the series include a GPS antenna connector, CLK OUT, PFI 0 / IRIG-B input, PFI 1, PFI 2, and RJ-45 Ethernet; the product flyer specifies three front-panel PFI lines for the PXI-6683H. https://download.ni.com/support/manuals/373656c.pdf https://www.ni.com/pdf/product-flyers/pxi-timing-and-synchronization-modules.pdf?srsltid=AfmBOor4OMn0cGr0ojwgdQuq9Qjkvv0b9gJWlTeDfgi8FVZ2djz15sBv https://www.ni.com/en/shop/hardware/system-timing/model-pxi-6683h
NI clearly distinguishes PXI-6683H from the base PXI-6683. According to the user manual, the PXI-6683H does not include PXI_STAR trigger lines, does not have CLKIN circuitry, and does not have the ability to drive PXI_CLK10_IN. NI also states that replacing PXI_CLK10 is not supported by the PXI-6683H, and the product page lists Backplane Clock Override as No. Additional NI page fields state Clock Import: No, Clock Export: Yes, and PXI_TRIG access: supported. These distinctions are important when matching the H variant to systems that need hybrid-slot installation but do not require timing-slot-only capabilities. https://download.ni.com/support/manuals/373656c.pdf https://www.ni.com/en/shop/hardware/system-timing/model-pxi-6683h
