Sequencer setup.
The sequencer has up to 7 programmable states which can be configured through this screen. When the sequencer is triggered it starts at the state configured in :SEQ:PC_S and counts down; when state 1 completes the sequencer programme is complete, unless the super-sequencer is also in use.
During operation of a single state, the sequencer will step the swept NCO through a series of frequencies as programmed by Sweep start, Sweep step, Capture above. Each frequency will be driven for Holdoff + Dwell time turns, and data may be captured from the detectors if appropriately configured.
Sequencer State Configuration
Each sequencer state is controlled by the following PVs.
| Title | PV | Description |
|---|---|---|
| Sweep start | :SEQ:n:START_FREQ_S | This sets the initial frequency for the swept NCO. All frequencies are in multiples of the machine revolution frequency. |
| Sweep step | :SEQ:n:STEP_FREQ_S | This sets the frequency advance when the sequencer steps from one dwell period to the next. |
| Sweep end | :SEQ:n:END_FREQ_S | This is automatically set to start+step*capture, and is automatically updated any time any of those values changes. If this PV is written to then step will be computed (as (end-start)/capture) and this PV will update. |
| Capture | :SEQ:n:COUNT_S | This configures the number of dwells in this sequencer state. |
| Holdoff | :SEQ:n:HOLDOFF_S | This number of turns is added to the start of the dwell time after the swept frequency has been stepped. The detector is disabled for the duration of the holdoff period, which can be used to give time for the swept system to settle to the new frequency. |
| Dwell time | :SEQ:n:DWELL_S | This configures the number of turns for which the sweep frequency is driven and the detector is operated for a single sample. |
| Magnitude | :SEQ:n:GAIN_S, :SEQ:n:ENABLE_S | This determines the gain of the swept NCO excitation in 6dB steps, with 0dB corresponding to full scale DAC excitation. :ENABLE_S must be set to "On" for a signal to be generated. |
| Bunch Bank | :SEQ:n:BANK_S | This determines which of the four available bunch configuration banks is selected during the operation of this state. |
| Blanking | :SEQ:n:BLANK_S | If this is set to "Blanking" then the detector will be temporarily disabled during the blanking window and the dwell time will be extended. |
| Data window | :SEQ:n:ENWIN_S | If this is set to "Windowed" then the detector data will be multiplied by the data window configured in Detector Window Setup. |
| Data capture | :SEQ:n:CAPTURE_S | This determines whether the detector is active during this sequencer state. |