National Instruments SC-2040 - Manual (Page 37)

Theory of Operation Chapter 4
SC-2040 User Manual 4-4 © National Instruments Corporation
find the inputs again after having been in hold mode. Therefore, this delay indicates how long
the SC-2040 must remain in track mode before it is ready to re-enter hold mode. Returning the
SC-2040 to hold mode before the track-mode acquisition delay has elapsed will cause the
SC-2040 to "hold" erroneously. Figure 4-2 illustrates these timing concerns. Typical hold mode
settling times and track acquisition times for 12-bit and 16-bit accuracies are given in
Appendix A, Specifications.
hold track hold
track
track acquisition
time hold setting time hold setting
time
differential channel
input
T/H output
track*/hold signal
(PF17)
Figure 4-2. T/H Amplifier Hold Settling Time and Track Acquisition Time
Triggering from the DAQ Board
This section applies to you only if you are triggering the SC-2040 from the MIO-16E board.
Note: No signal should be connected to connector J10 for MIO-16E triggering.
You can place the SC-2040 into hold mode on command using the MIO-16E DAQ board. You
must either program the MIO-16E board for this purpose or use the NI-DAQ software included
with your MIO board. After placing the SC-2040 into hold mode, the MIO-16E board performs
data acquisition and conversion. Once this process is complete, the MIO-16E board releases the
SC-2040 into track mode.
The MIO-16E board uses line PFI7/STARTSCAN to indicate to the SC-2040 whether it should
track the input signals or hold them at a constant level. A logic zero (low level) on
PFI7/STARTSCAN indicates track mode, while a logic one (high level) indicates hold mode, as
indicated in Figure 4-3.