Chapter4 SignalConnections
©NationalInstruments Corporation 4-49 6023E/6024E/6025EUser Manual
Ifyou use an internal timebaseclock, the gate signal cannot be
synchronized with the clock. In this case, gates applied close to a source
edge takeeffect either on that source edge or on the next one. This
arrangement results in an uncertainty of one source clock period with
respectt o unsynchronized gating sources.
The OUT output timing parameters arereferenced to the signal at the
SOURCE input or to one of the internally generated clock signals on the
devices.Figure 4-41 shows the OUT signal referenced to the rising edge of
asource signal. Any OUT signal st ate changes occur within 80 ns after the
rising or falling edge of the source signal.

FREQ_OUT Signal

This signal is available only as an output on the FREQ_OUT pin. The
frequency generator of the device outputs the FREQ_OUT pin. The
frequencygenerator is a 4-bit cou nter that can divide its input clock by the
numbers 1 through 16. The input clock of the frequency generator is
software-selectablefrom the internal 10 MHzand 100 kHz timebases. The
outputpolarity is software-sel ectable. This output is set to high impedance
atstartup.
Field Wiring Considerations
Environmentalnoise can seriously affect the accuracy of measurements
made with your device if you do not take proper care when running
signal wires between signal sources and the device. The following
recommendationsapply mainly to analog input signal routing to the device,
although they also apply to signal routing in general.
Minimizenoise pickup and maximize measurement accuracy by taking the
followingprecautions:
•Use DIFF analog input connections to reject common-mode noise.
•Use individuallyshielded, twisted-pai rwires to connect anal og input
signalsto the device. With this type of wire, the signals attached to the
CH+ and CH–inputsare twisted together and then covered with a
shield. Youthen connect this shield only at one point to the signal
sourceground. This kind of connection is required for signals traveling
through areas with largemagnetic fields or high electromagnetic
interference.