The DAQ Trigger

The DAQ Trigger interfaces 'experiment's trigger' with the Data Acquisition System. It tells the DAQ when and what type of trigger needs to be taken. The DAQ trigger logic implements the beam gate (using the AGS timing signals), 6 different types of triggers and provides the 'DAQ busy' and the 'slow enable' signals to the outside world. Each of the six triggers can be individually enabled or disabled using the 'loadTrigger' program (the 'other->set trigger' button in the DAQcontrol program).

The DAQ trigger logic is implemented in one LeCroy 2372 MLU, with a few NIM modules (NIM-ECL converters, flip-flops, one-shots and blinkenlights).

DAQ Trigger Types

The E852 DAQ code implements 8 different triggers. Each trigger is programmed to readout it's own set of Fastbus and CAMAC devices. The trigger type of any event can be found in the 'event->trigger' member of the event header (itape_header_t structure). Trigger 0 is BOS (Begin of spill or BSPI), trigger (-1) is EOS (end of spill or ESPI) with remaining triggers numbered from 1 through 6.

Internal and external signals

beam gate - the beam gate signal is provided by the beam gate flip-flop. This flip-flop is driven by the 'PreDat' (programmed dalay) device in the MPS control room. The PreDat is driven by the AGS-provided clock.
SSP start - The SSP start signal starts the Master SSP. The master SSP should be restarted only when it expects to be restarted, otherwise all the hell will break loose.
SSP done - one of the signals provided by the master SSP to control the trigger. The master SSP should never be started by the 'SSP start' signal when the 'SSP done' is not 'ON'. The 'Done' LED on the front panel of the master SSP shows the state of the 'SSP done' signal.
DAQ busy - signal controlled by the MLU and the trigger latch. When a trigger is taken, the MLU sets the 'busy' signal ON, it is latched in the trigger latch, feeds through the latch back into the MLU and disables any further triggers. When the DAQ is ready, the master SSP clears the trigger latch which resets the 'DAQ busy' signal back to the 'OFF' state.
triggers - the external triggers are fed to the MLU through one-shots (discriminator) to prevent a race-condition with the busy signal.
trigger type - the trigger type is a three-bit - encoded number from 0 to 7. 0 through 5 are normal triggers, 6 and 7 are BOS and EOS.

DAQ Trigger Parts

The DAQ trigger is made of the following parts:

Master SSP - the Master SSP controls the DAQ during the event taking phase of the spill.
beam gate flip-flop - triggers are taken only when the beam gate is 'on'
trigger one-shots - to avoid a race condition and be independant from the trigger pulse lengths, all the triggers are fed through a one-shot (discriminator).
trigger latch - the DAQ (Master SSP) uses the latch to output a set of 'enable' signals: enable BOS, enable EOS, enable Fast and enable Slow. The trigger type and the busy signal are latched into the trigger latch to tell the master SSP that a trigger needs to be taken.
LeCroy 2372 MLU - is fed the 'trigger', 'enable' and 'busy' signals described above and decides if the master SSP should be started.

Wiring diagram


                      LC 4616 NIM-ECL       LC 2372 MLU            Str136 Latch
                          |-----|            |-----|                 |-----|
beam gate (NIM level) --->|  1  |----------->|  0  |---> trigger --->|  0  |----> wires 0
 trigger1 (NIM pulse) --->|  2  |----------->|  1  |--->  type   --->|  1  |- through 6 are
 trigger2 (NIM pulse) --->|  3  |----------->|  2  |---------------->|  2  |- not connected
 trigger3 (NIM pulse) --->|  4  |----------->|  3  |- unused         |  3  |-
 trigger4 (NIM pulse) --->|  5  |----------->|  4  |---> SSP start ->|  4  |-
 trigger5 (NIM pulse) --->|  6  |----------->|  5  |-                |  5  |-
 trigger6 (NIM pulse) --->|  7  |----------->|  6  |-  5 through     |  6  |-
     enable EOS (ECL) --->|  8  |----------->|  7  |- 10 - unused    |  7  |----> enable EOS ---> wires 7
     enable BOS (ECL) --->|  9  |----------->|  8  |                 |  8  |----> enable BOS ---> through 15 loop
    enable Slow (ECL) --->| 10  |----------->|  9  |                 |  9  |----> enable Slow --> back into
    enable Fast (ECL) --->| 11  |----------->| 10  |                 | 10  |----> enable Fast --> the ECL-NIM-ECL
           busy (ECL) --->| 12  |----------->| 11  |---> busy ------>| 11  |----> busy ---------> converter
  not(SSP done) (NIM) --->| 12  |            |     |                 |     |
      SSP start (ECL) --->| 13  |------      | 12  |---> SSP start ->| 12  |----> SSP start ---->
                          | 14  |     |      | 13  |                 | 13  |
       BOS (from MLU) --->| 15  |     |      | 14  |---------------->| 14  |----> BOS (feed through)
       EOS (from MLU) --->| 16  |     |      | 15  |---------------->| 15  |----> EOS (feed through)
                          |-----|     |      |-----|                 |-----|
                                      |
                                      V
                              Master SSP start

Note0: On the LC 4616 device, the pins are numbered starting from one. On the MLU and Latch, the inputs
       (bits) are numbered from zero (the usual convention - bit0 through bit15).
Note1: the (ECL) 'busy' and (NIM) 'not (SSP done)' signals are or'ed on the NIM-ECL coverter pin 12.

MLU programming

The MLU is operating in 'transparent' mode. The latch is operating with the gate always open and is reset by the master SSP.

'busy'

When the 'busy' signal is ON, all the MLU output are OFF.

beam gate

When the 'beam gate' is ON, the 'BOS enable' is ON and 'busy' is OFF, the MLU generates a BOS trigger.

When the 'beam gate' is OFF, the 'EOS enable' is ON and 'busy' is OFF, the logic generates an EOS trigger.

trigger

When one and only one of the trigger inputs is ON and ('enable Slow' or 'enable Fast' are ON) and 'busy' is OFF, a trigger is generated. When a trigger is generated, the MLU sets the trigger type bits, and turns the 'busy' and the 'SSP start' outputs ON.

Related files

$E852DAQROOT/bin/loadDaqTrigger       - load and configure the LC2372 MLU.
$E852DAQROOT/init/mlu_daqTrigger.perl - the MLU program macrogenerator
$E852DAQROOT/bin/write2372            - the MLU loader
man mlu_logic

For additional information please contact me (Const Olchanski)

//end file