Second Level Trigger Control

We have considered the control of the CTD-SLT in terms of communications. The SLT can be view to communicate in three ways: 1) internally within the CTD-SLT itself, 2) with other CTD readout systems like the global CTD readout transputer and ROC's, and 3) with the outside world via the GSLTB. Since the GSLTB communicates to the CTD via the EVB and the CTD-SLT is not connected directly to the EVB, the CTD-SLT is only concerned with internal control and control within the CTD readout system (harness channels). Hence control signals can come to the SLT via either the data stream or from the harness. Internal SLT control was discussed previously.

The control of the SLT follows closely that of run sequencing. The actions the SLT will take according to the run state are listed as follows.

• BEGIN-OF-RUN
  1. Harness sends SLT a setup signal (monitoring may be controlled here).
  2. SLT acknowledges setup to harness.
  3. SLT receives begin-of-run (BOR) signal from harness.
  4. SLT sends BOR event to EVB (via harness).
  - SLT awaits arrival of data from ROC's.
• PAUSE RUN - Data stops flowing to SLT (monitoring may be controlled here).
• RESUME RUN (after PAUSE) - Data flows from ROC's to SLT.
• END RUN (immediately after PAUSE) - Follow steps as in end-of-run (EOR).
• END-OF-RUN
  1. SLT receives EOR trigger/data type from ROC's.
  2. SLT sends EOR trigger to GSLTB.
  3. SLT sends EOR event to EVB (via harness).
  - Data stops flowing from ROC's to SLT.

Figure 3 shows state transition diagrams of the CTD-SLT system. The EOR signal is derived from the data, while the setup, BOR and monitor control signals arrive over harness channels.

 
Figure 3:   CTD-SLT State Transition Diagrams.

 
Figure 4: (continued) CTD-SLT State Transition Diagrams.