Chapter 4
Programming
© National Instruments Corporation
4-51
AT-MIO-16D User Manual
An overrun condition occurs if an A/D conversion is initiated before the previous conversion is
finished. This condition may result in one or more missing A/D conversions. This condition
occurs if the sample interval is too small (sample rate is too high). An overrun condition has
occurred if the OVERRUN bit in the Status Register is set. The maximum recommended single-
channel data acquisition rate for the AT-MIO-16D is 100 ksamples/sec.
Both the OVERFLOW and OVERRUN bits in the Status Register are cleared by writing to the
A/D Clear Register.
External Timing Considerations for Multiple A/D Conversions
The case of controlled data acquisition operations using the onboard sample-interval and sample
counters was described above. The two external timing cases are described here–using the STOP
TRIG input to control the sample counter, and applying pulses to the EXTCONV* input.
Pretriggering with the STOP TRIG Signal
In this case, the sample-interval counter starts counting when a rising edge signal is applied to
the STOP TRIG input on the AT-MIO-16D I/O connector. You program the sample counter for
active high level gating on Gate 4. The data acquisition operation is initiated by writing to the
Start DAQ Register or by a pulse on the START TRIG* input. The sample count register does
not begin counting samples until a rising edge is applied to STOP TRIG. To perform this
operation, complete these steps:
1. Select analog input channel and gain.
2. Program the sample-interval counter.
3. Program the sample counter.
4. Clear the A/D circuitry.
5. Apply a trigger.
6. Service the data acquisition operation.
1. Select analog input channel and gain.
The analog input channel and gain are selected by writing to the Mux-Gain Register. Bits 7 and
6 control the gain, and bits 3 through 0 select the analog input channel. See the Mux-Gain
Register bit description earlier in this chapter for gain and analog input channel bit patterns. Set
up the bits as given in the Mux-Gain Register bit description, and write to the Mux-Gain
Register.
Once set up with an initial value, the Mux-Gain Register needs to be written to only when you
need to change the analog input channel or gain setting.
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