PXI, PXI Express, PCI, and PCI Express NI-XNET

The PXI and PXI Express chassis features a dedicated synchronization bus integrated into the backplane. NI-XNET products support use of this bus to synchronize with other NI hardware products such as DAQ, IMAQ, and motion. The PXI synchronization bus consists of a flexible interconnect scheme for sharing timing and triggering signals in a system.

For PCI and PCI Express hardware, the RTSI bus interface is a connector at the top of the card. You can synchronize multiple National Instruments PCI/PCIe cards by connecting a RTSI ribbon cable between the cards that need to share timing and triggering signals.

CAN/XS, PCIe-8510 (4-Port), and FlexRay XNET products also feature two configurable timing and triggering ports on the device front panel. These ports are TTL-tolerant user-configurable for inputting and outputting timebases and triggers. These signals are not electrically isolated from the backplane. Refer to the XNET Connect Terminals function documentation for more details.

C Series NI-XNET

All NI-XNET ports on a particular C Series chassis share a common timebase, allowing a better correlation of data on the ports. NI-XNET products support use of this timebase to synchronize with other National Instruments hardware products such as DAQ modules.

Moreover, on a CompactRIO system, the module's timebase is corrected for drift with respect to the RT controller's timebase, allowing the capability to correlate data with other modules in the chassis.

On a CompactDAQ system, you can route the Start Trigger between multiple DAQmx and XNET modules. For information about performing this routing in LabVIEW, refer to the LabVIEW API Interface:Source Terminal:Start Trigger property. For information about performing this routing in C/C++, refer to the C API Interface:Source Terminal:Start Trigger property.

USB NI-XNET

USB-850x 2-port devices can synchronize with external trigger or clock sources. Synchronization occurs through a 3-pin Combicon connection allowing for a shared timestamp clock, start trigger, and ground. USB-850x 2-port devices can synchronize to timestamp clocks of 20 MHz, 10 MHz, or 1 MHz. For 20 MHz synchronization, ensure that the synchronization cable is shielded and grounded. Clock frequency is detected automatically by the hardware, and illegal clock frequencies are reported as an error. USB-850 x 2-port devices can also generate a clock of 1 MHz, allowing for accurate CAN-CAN, CAN-LIN, and LIN-LIN synchronization.

Automotive Ethernet NI-XNET

  • Local Time—

    NI Automotive Ethernet modules use PXI_Clk10, a 10 MHz PXI backplane clock provided by the chassis, to drive the local time keeper and to synchronize with other modules in the PXI chassis. If the PXI backplane clock is not available, the module uses its own internal oscillator.

    PXI_Clk10 provides frequency but not date/time information. When an NI-XNET session is created, XNET initializes the date/time information for the local clock using host time.

  • Network Time—

    NI Automotive Ethernet modules can also maintain network time (IEEE 802.1AS) for each port. When Ethernet frames are received, each packet is time stamped with network time as well as with local time.

    When a port acts as a master, the network time is initialized from host time and is synchronized to local time.

    When a port acts as a slave in an electronic control unit (ECU) network, local time and network time can eventually drift, relative to each other. The date/time information for network time is obtained from the ECU that acts as the grandmaster clock.

    Both local and network time can be adjusted using the NI-XNET API.

  • Host Time—

    Host time is the clock of the operating system where LabVIEW is running. The host time can obtain time/date information using a real time clock (RTC) or a network time protocol (NTP) server.

    Although host time provides accurate date/time information, the accuracy and resolution of its clock can often be in tens of milliseconds. In contrast, NI Automotive Ethernet modules provide resolution for local time and network time in nanoseconds. Although local time and network time use host time to initialize their date/time information, they do not use the same physical clock as host time. Therefore, both local time and network time can eventually drift relative to host time.

  • Triggers—

    Triggers can be simultaneously time stamped by the local time keeper and the network time keeper for each port. PXI triggers can be used to synchronize the NI Automotive Ethernet module's time keepers with trigger events on other PXI modules.