Exporting a Clock
The NI 655x provides several resources for exporting clocks. The Clocking block diagram shows how the NI 655x 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 CLK OUT and the Sample clock to DDC CLK OUT. |
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 on DDC connector |
| CLK OUT | CLK OUT SMB jack connector | |
| Reference Clock | CLK OUT | CLK OUT SMB jack connector |
| Onboard Reference Clock (NI PCI-655x only) | RTSI 7 | RTSI trigger bus channel 7 |
Sample Clock
The Sample clock can be exported to one of two destinations: the DDC CLK OUT pin on the DDC connector or the CLK OUT SMB jack connector.
- DDC CLK OUT—The Sample clock can be exported to the CLK OUT pin on the DDC connector. The exported Sample clock is generated at the same 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.
- CLK OUT—The Sample clock can be exported to the CLK OUT SMB connector. The exported Sample clock is generated at the same voltage levels specified for dynamic generation.
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 655x, you can export the reference clock to the CLK OUT SMB jack connector. The exported reference clock operates at 3.3 V logic, independent of the rest of your programmed channels, DIO<0..19>.
Onboard Reference Clock
If you are using an NI PCI-655x, 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.