Exporting a Clock
The NI 656x provides several resources for exporting clocks. The Clocking block diagram shows how the NI 656x exports these clocks.
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Note As shown in the clocking block diagram, it is possible to export both the Reference clock and the Sample clock at the same time if you route the Reference clock to the CLK OUT SMB jack connector and the Sample clock to DDC CLK OUT channel on the DDC connector. You cannot route the Sample clock to both connectors. |
For information about using NI-HSDIO to export clocks, refer to the niHSDIO Export Signal VI or the niHSDIO_ExportSignal function.
The following table summarizes the possible exported clock options.
| Clock | Destination | Description |
|---|---|---|
| Sample Clock | DDC CLK OUT | DDC CLK OUT LVDS and DDC CLK OUT LVPECL on DDC connector |
| CLK OUT | CLK OUT SMB jack connector | |
| Reference Clock | CLK OUT | CLK OUT SMB jack connector |
| Onboard Reference Clock (NI PXI-656x only) | RTSI 7 | RTSI trigger bus channel 7 |
Sample Clock
The Sample clock can be exported to one of two destinations: the DDC connector or the CLK OUT SMB jack connector.
- DDC CLK OUT—The Sample clock can be exported to the DDC CLK OUT
on the DDC connector. The exported Sample clock is generated at the logic family voltage levels
specified for dynamic generation. For dynamic generation sessions, exporting the Sample
clock to this connector allows for source-synchronous clocking by routing the Sample clock
through the same cable and propagation delay characteristics as the generated data.
Note When the Sample clock is exported to the DDC connector, both an LVDS and an LVPECL version of the clock signal are exported. - CLK OUT—The Sample clock can be exported to the CLK OUT SMB jack connector. Refer to the NI 656x specifications for more information about the voltage levels for the exported Sample clock.
You can export the Sample clock to either the DDC connector or the CLK OUT SMB jack connector, but not at the same time.
Reference Clock
If you configure a reference clock for the PLL on the NI 656x, you can export the reference clock to the CLK OUT SMB jack connector. Refer to the NI 656x specifications for more information about the voltage levels for the exported Reference clock.
Onboard Reference Clock
If you are using an NI PCI-656x, you can export the 10 MHz onboard reference clock to RTSI 7 on the RTSI trigger bus. You can then use a RTSI cable to connect this signal to other PCI devices.