Chapter 3
Hardware Overview
6711/6713/6715 User Manual
3-4
www.ni.com
Analog Output
The 6711 has four channels and the 6713/6715 has eight channels of
voltage output at the I/O connector. The reference for the analog output
circuitry is software selectable per channel. The reference can be either
internal or external, whereas the range is always bipolar. This means that
you can output signals up to ±10 V with internal reference selected or ±
EXTREF voltage with external reference selected.
Analog Output Reference Selection
You can connect each D/A converter (DAC) to the internal reference of
10 V or to the external reference signal connected to the external reference
(EXTREF) pin on the I/O connector. This signal applied to EXTREF
should be within ±11 V of AOGND. You can configure each channel to use
either internal or external reference. The default reference value selection
is internal reference.
Analog Output Reglitch Selection
In normal operation, a DAC output will glitch whenever it is updated with
a new value. The glitch energy differs from code to code and appears as
distortion in the frequency spectrum. Each analog output channel contains
a reglitch circuit that generates uniform glitch energy at every code rather
than large glitches at the major code transitions. This uniform glitch energy
appears as a multiple of the update rate in the frequency spectrum. Notice
that this reglitch circuit does not eliminate the glitches; it only makes them
more uniform in size. By default, reglitching is disabled for all channels,
however you can use NI-DAQ to independently enable reglitching for each
channel.
Digital I/O
The 671X device contains eight lines of digital I/O for general-purpose use.
You can individually software-configure each line for either input or
output. At system startup and reset, the digital I/O ports are all high
impedance.
The hardware up/down control for general-purpose counters 0 and 1 are
connected onboard to DIO6 and DIO7, respectively. Thus, you can use
DIO6 and DIO7 to control the general-purpose counters. The up/down
control signals are input only and do not affect the operation of the
DIO lines.
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