National Instruments AT E Series - Manual (Page 87)

Chapter 4 Connecting Signals
AT E Series User Manual 4-40 ni.com
Either the 20 MHz or 100 kHz internal timebase generates the SISOURCE
signal unless you select some external source. Figure 4-23 shows the
timing requirements for the SISOURCE signal.
Figure 4-23. SISOURCE Signal Timing
SCANCLK Signal
SCANCLK is an output-only signal that generates a pulse with the leading
edge occurring approximately 50 to 100 ns after an A/D conversion begins.
The polarity of this output is software selectable but is typically configured
so that a low-to-high leading edge can clock external AI multiplexers
indicating when the input signal has been sampled and can be removed.
This signal has a 400 to 500 ns pulse width and is software enabled.
Figure 4-24 shows the timing for the SCANCLK signal.
Note When using NI-DAQ, SCANCLK polarity is low-to-high and cannot be changed
programmatically.
Figure 4-24. SCANCLK Signal Timing
t
w
= 23 ns minimum
t
p
= 50 ns minimum
t
w
t
w
t
p
t
w
= 400 to 500 ns
t
d
= 50 to 100 ns
CONVERT*
SCANCLK
t
d
t
w