Chapter 4 Analog Input© National Instruments Corporation 4-25 NI 6232/6233 User Manualsources for ai/SampleClock. You can configure the polarity selection forai/SampleClockTimebase as either rising or falling edge.AI Convert Clock SignalUse the AI Convert Clock (ai/ConvertClock) signal to initiate a single A/Dconversion on a single channel. A sample, controlled by the AI SampleClock, consists of one or more conversions.You can specify either an internal or external signal as the source ofai/ConvertClock. You also can specify whether the measurement samplebegins on the rising edge or falling edge of ai/ConvertClock.With NI-DAQmx, the driver will choose the fastest conversion rate possiblebased on the speed of the A/D converter and add 10 μs of padding betweeneach channel to allow for adequate settling time. This scheme enables thechannels to approximate simultaneous sampling and still allow foradequate settling time. If the AI Sample Clock rate is too fast to allow forthis 10 μs of padding, NI-DAQmx will choose the conversion rate so thatthe AI Convert Clock pulses are evenly spaced throughout the sample.To explicitly specify the conversion rate, use the AI Convert Clock RateDAQmx Timing property node or function.Caution Setting the conversion rate higher than the maximum rate specified for yourdevice will result in errors.Using an Internal SourceOne of the following internal signals can drive ai/ConvertClock:• AI Convert Clock Timebase (divided down)• Counter n Internal OutputA programmable internal counter divides down the AI Convert ClockTimebase to generate ai/ConvertClock. The counter is started byai/SampleClock and continues to count down to zero, produces anai/ConvertClock, reloads itself, and repeats the process until the sample isfinished. It then reloads itself in preparation for the next ai/SampleClockpulse.
