Clocking

The clocks on the NI 6589 control the sample rate and other timing functions on your FlexRIO system. The following figure shows the NI 6589 clock sources routed through the crosspoint switch. The Generation Bank I/O clock, PFI Bank I/O clock, and Global clock are all sourced by the crosspoint switch. The Acquisition Bank I/O clock can be sourced from the crosspoint switch or accessed directly through the Strobe Bypass path.

Note Only the Acq_IO_Clock_Source signal can use the STROBE Bypass path. If Acq_IO_Clock_Source is set to Strobe Bypass, then Gen_IO_Clock_Source, PFI_IO_Clock_Source, and IO_Module_Clock_1_Source cannot be set to Strobe From Crosspoint Switch.
Figure 11. Crosspoint Switch


In software, each clock output terminal is accessed with a U8 data type. The following table shows the values of the crosspoint switch clock options.

Table 6. Clock Values
Value Clock Option
0 Tristate—Output disabled (high impedance).
2 Sync Clock (PXI Express Only)—Clock from PXI Express backplane. You can select PXI_CLK10 or DStarA in the Details category of the IO Module Properties dialog box.
3 Adapter Module Onboard Clock—Clock generated from the Si570 clock chip.
4 Strobe From Crosspoint Switch—LVDS STROBE signal from crosspoint switch. Use this setting to route the LVDS STROBE signal to multiple I/O clocks.
5 Strobe Bypass—LVDS STROBE bypasses the crosspoint switch. The propagation delay of the Strobe Bypass exactly matches the propagation delay of the data channels. This setting is ideal for source- synchronous applications.