New PiLC Feature: Trigger Arrays

These are continuous scan requirements raised by P02, P21, P23.

• The continuous scan is executed as a sequence regions with the shutter being OPEN or CLOSED.

• The PiLC has to generate a gate signal for the shutter.

• The PiLC has to generate a signal which triggers the read-out of the Perkin Elmer detector. A read-out sequence clears the detector. Depending on the circumstances the read-out has to be repeated several times to ensure that the PE is really cleared.

  The PE read-out happens when the shutter is closed.

• In order to cover the full angular range, the scan has to be repeated. The OPEN regions of the second sweep are the CLOSED regions of the first.

• Other detectors may be used that need other trigger signals.

In order to fulfill an arbitray scheme of triggers and gates, the follwoing PiLC feature has been discussed:

• The status of certain PiLC output lines (trigger lines) is defined by two arrays containing encoder positions (or counter values) and action flags (under discussion).

• The values in the first array specify when an action is to be taken.

• The values in the second array specify what has to be done. So far: output HIGH or LOW.

• There can be several trigger outputs, so far 4.

• Each trigger output needs 2 arrays.

• At most 4 million trigger points can be specified.

• Two input lines are reserved for the encoder input signals.