Chapter 2 Analog Input
© National Instruments Corporation 2-45 E Series User Manual
AI Convert Clock Timebase Signal
Either the ai/SampleClockTimebase or the MasterTimebase signal can
serve as the source of the AI Convert Clock Timebase signal
(ai/ConvertClockTimebase), which is not available as an output on the I/O
connector. The ai/ConvertClockTimebase is divided down to provide the
Onboard Clock source for the ai/ConvertClock.
Master Timebase Signal
The Master Timebase (MasterTimebase) signal, or Onboard Clock, is the
timebase from which all other internally generated clocks and timebases on
the board are derived. It controls the timing for the analog input, analog
output, and counter subsystems. It is available as an output on the I/O
connector, but you must use one or more counters to do so.
The maximum allowed frequency for the MasterTimebase is 20 MHz, with
a minimum pulse width of 23 ns high or low. There is no minimum
frequency limitation.
The two possible sources for the MasterTimebase signal are the internal
20MHzTimebase signal or an external signal through RTSI 7. Typically the
20MHzTimebase signal is used as the MasterTimebase unless you wish to
synchronize multiple devices, in which case, you should use RTSI 7. Refer
to Chapter 8,
Real-Time System Integration Bus (RTSI), for more
information about which signals are available through RTSI.
Figure 2-33 shows the timing requirements for MasterTimebase.
Figure 2-33. MasterTimebase Timing Requirements
t
p
= 50 ns minimum
t
w
= 23 ns minimum
t
w
t
w
t
p
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