5.3.2 Random Polarization ScramblingThe scrambler operation is activated by double-clicking the sub-itemScramble of the A3XXX instrument. This will also show a dialog forsetting the parameters of the scrambler.For simple asynchronous operation turn Timebase to Timer and choosea repetition rate. The repetition rate is the clock used for processing thelook-up-table. If the field Prescaler is greater than 0, the clock is dividedby Prescaler+1.Scrambling is implemented by generating a special look-up-table. The ta-ble length can be chosen by the field Seq. Length. Larger values make thepolarization controller steps smaller and increase the size of the look-up-table. By pressing the Randomize button, the current pattern is replacedby a new set of random SOPs.If Synchronization is set to Auto Repeat, the scrambling sequence is pro-cessed repeatedly without any external synchronization.If Synchronization is set to Auto Oneshot, the scrambling sequence isprocessed just once. The polarization controller remains on the last tableentry.If Synchronization is set to External Repeat or External Oneshot, thebehavior is similar except that the sequence is restarted when a low/hightransition occurs at the Trigger Input #1. The exact time relative tothe external trigger signal can be adjusted using the Hold off time. Thisvalue defines the delay between the trigger pulse and the restart of thesequence.The external trigger signal can be used as timebase instead of the internaltimer. In this mode the look-up-table is processed at the clock rateapplied to Trigger Input #1. Turn Timebase to External to activate thisfunction.With the external timebase a restart of the sequence can be achievedby applying a TTL signal to Trigger Input #2. This input is not edge-triggered, therefore a high level of at least 100 μs duration triggers arestart of the sequence on the next rising edge of Trigger Input #1.30 A1XXX/A2XXX/A3XXX User Guide
