Note It is recommended that pre-arm readings use the faster of the two sample rates. One additional sample pulse at the pre-arm rate, after the arm occurs, is required for the sample rate to change. The digitizer does not sample on this additional pulse. Post-arm sample pulses may be ignored depending on how fast they occur following the rate change. Refer to Appendix A - "Specifications", for additional information on dual rate sampling characteristics.

The Digitizer Reference Clock

When the digitizer trigger source is TIMer or DTIM (dual rate sampling), the sample (reading) rate is derived from a reference clock (Figure 3-5). The commands used to select the clock source and its frequency are part of the SENSe subsystem:

SENSe[<chan >] :ROSCillator

:EXTernal

:FREQuency <frequency > :SOURce <source >

Setting the Reference The reference source is set with the command:

Source

SENSe[<chan >]:ROSCillator:SOURce <source >

Specifying the External Reference Frequency

The reference sources are:

CLK10 - the VXIbus 10 MHz clock.

ECLTrg0 - the VXIbus ECLTRG 0 trigger line.

ECLTrg1 - the VXIbus ECLTRG 1 trigger line.

EXTernal2 - the digitizer’s Ext 2 BNC port.

INTernal - the digitizer’s internal 20 MHz oscillator. This is the default source.

When the trigger source is TIMer or DTIM, and the clock source is one of the following:

ECLTrg0

ECLTrg1

EXTernal2

the digitizer processor must be informed of the reference frequency in order for TRIGger:STARt:TIMer1 or TRIGger:STARt:TIMer2 to generate the correct sample rate. This is done with the command:

SENSe[<chan >]:ROSCillator:EXTernal:FREQuency <frequency >

124 Understanding the HP E1429 Digitizer

Chapter 3

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HP E1429A manual Digitizer Reference Clock, Source, Specifying the External Reference Frequency