Analog Output Timing Connections - DAQ DAQCard-1200 User Manual

Chapter 3 Connecting the Signals
OUTB1
EXTCONV*
CONVERT
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DAQCard-1200 User Manual
t = 50 ns
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t = 50 ns
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Figure 3-16. Interval-Scanning Signal Timing

Analog Output Timing Connections

Counter A2 is used to internally control updating the output voltage of the
12-bit DACs. In place of counter A2, you can use the final external control
signal, EXTUPDATE*, to externally control updating the output voltage of
the 12-bit DACs and/or to generate an externally timed interrupt. There are
two update modes—immediate update and delayed update. In immediate
update mode the analog output is updated as soon as a value is written to
the DAC. If you select the delayed update mode, a value is written to the
DAC; however, the corresponding DAC voltage is not updated until a low
level on the EXTUPDATE* signal or counter A2 is sensed. Furthermore,
an interrupt is generated whenever a rising edge is detected on the
EXTUPDATE* bit. The interrupt service routine can write the next value
to the DAC. When the EXTUPDATE* signal goes low, the DAC is
subsequently updated. Therefore, you can perform externally timed
interrupt-driven waveform generation on the DAQCard-1200.
Notice that the EXTUPDATE* signal is level sensitive; that is, if you
perform writes to the DAC when EXTUPDATE* is low, the DAC is updated
immediately. Also notice that when EXTUPDATE* is low, the signal is
susceptible to noise caused by switching of other lines. Because the signal
is TTL-compatible, the lower noise margin for logical 0 can result in
transitions to a logical 1 due to noise and thereby generate false interrupts.
Therefore, the width of EXTUPDATE* pulse should be as short as
possible, but greater than 50 ns.
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