Figure 311. pretrigger daq timing, Figure 3-11, Pretrigger daq timing -21 – National Instruments PCI-1200 User Manual
Page 43
Chapter 3
Signal Connections
© National Instruments Corporation
3-21
Figure 3-11. Pretrigger DAQ Timing
For interval scanning data acquisition, counter B1 determines the scan
interval. Instead of using counter B1, you can externally time the scan
interval through OUTB1. If you externally time the sample interval, we
recommend that you also externally time the scan interval.
Figure 3-12 shows an example of an interval scanning DAQ operation. The
scan interval and the sample interval are being timed externally through
OUTB1 and EXTCONV*. Channels 1 and 0 of the input multiplexers are
scanned once during each scan interval. The first rising edge of
EXTCONV* must occur a minimum of 50 ns after the rising edge on
OUTB1. The first rising edge of EXTCONV* after the rising edge of
OUTB1 enables an internal GATE signal that allows conversions to occur.
The first conversion then occurs on the following falling edge of
EXTCONV*. The GATE signal disables conversions for the rest of the scan
interval after the desired channels have been scanned. Refer to the
section in Chapter 4,
, for
more information on interval scanning.
t
w
50 ns minimum
EXTTRIG
EXTCONV*
CONVERT
V
IH
V
IL
t
w
t
w