Sampling

Requirement: Sampling Rate and Procedure

The SCA shall sample PASA output data when the R/W control signal is active in the W (write) state. The SCA shall continuously sample input data on all channels simultaneously at a rate of 273 million samples per second. The newest data shall overwrite the oldest data. Switching the R/W control signal to R (read) will stop SCA sampling and freeze the last 128 samples pending readout. Timing for this is controlled by the Trigger subsystem.

Justification:

The sample rate is determined by physics resolution requirements. The need for continuous sampling arises because there is insufficient time after an event occurrence for the trigger system to generate a write trigger signal. Timing for the switching of the R/W signal to read is controlled by the Trigger subsystem because the Trigger subsystem has sampled and determined the likelihood that an event is interesting using fast detectors before the charge from that event has completely drifted through the SDD.

Requirement: Write Pointer Reset

The write pointer shall be reset to one cell called the fiducial cell at the start of a write cycle.

Justification:

This permits tracking and correcting stored charge pedestals.