National Instruments DAQCard-1200 - Manual (Page 65)

Chapter 4 Theory of Operation
DAQCard-1200 User Manual 4-12 © National Instruments Corporation
Power-On State
Both analog outputs reach 0 V approximately 110 ms after card insertion.
During this 110 ms period, the output voltage can swing from +2 to –5 V.
Warning Disconnect the analog outputs from the system before inserting the card in the
PC Card slot. This step ensures that you do not damage your system during the
110 ms before the output reaches 0 V.
DAC Timing
There are two ways you can update the DAC voltages. In the first mode,
the DAC output voltage is updated as soon as you write to the
corresponding DAC. This is called the immediate update mode. In the
second mode, the DAC output voltage does not change until a low level
is detected either from counter A2 of the timing circuitry or from
EXTUPDATE*. This mode is useful for waveform generation. These
two modes are software selectable.
Note Configure both the DACs in either immediate update mode or later update mode.
Do not configure the DACs in a combination of both modes because doing so can
result in premature updates on the waveform generation DAC (whenever the
immediate update DAC is updated). Also, if a waveform generation update occurs
between an LSB write and an MSB write of the DAC in the immediate update
mode, you will receive an incorrect value from that DAC until the MSB is written.
Both of these effects are minimal at high waveform update rates.