© National Instruments Corporation 12-1 NI USB-621x User Manual
12
Digital Routing and Clock
Generation
The digital routing circuitry has the following main functions.
• Manages the flow of data between the bus interface and the
acquisition/generation sub-systems (analog input, analog output,
digital I/O, and the counters). The digital routing circuitry uses FIFOs
(if present) in each sub-system to ensure efficient data movement.
• Routes timing and control signals. The acquisition/generation
sub-systems use these signals to manage acquisitions and generations.
These signals can come from the following sources.
– Your M Series device
– User input through the PFI terminals
• Routes and generates the main clock signals for the M Series device.
80 MHz Timebase
The 80 MHz Timebase can be used as the Source input to the 32-bit
general-purpose counter/timers.
The 80 MHz Timebase is generated from the onboard oscillator.
20 MHz Timebase
The 20 MHz Timebase normally generates many of the AI and AO timing
signals. The 20 MHz Timebase also can be used as the Source input to the
32-bit general-purpose counter/timers.
The 20 MHz Timebase is generated by dividing down the 80 MHz
Timebase.
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