The trigger electronics has switchable 63.5 ns delays on the hodoscope
OR's for both spectrometers. This allows one spectrometer to be delayed
by up to 63.5 ns with respect to the other. For the purposes of computing
the range of velocities that can be brought into coincidence, these delays
shall be considered to have a range of at most 
50 ns. This is to
allow room for making either spectrometer come slightly later than the
other and room to adjust the relative timing of the hodoscope planes.
Each spectrometer has essentially identical focal plane trigger logic. Each hodoscope signal is discriminated with a Phillips 16 Channel Discriminator Latch (CAMAC Model 7106). Because there is some cross talk within each group of 4 channels of this discriminator, the inputs are shuffled so that for single track events, only at most one input of each four channel group will have a hit. For each of the 4 hodoscope planes, the tubes on the two sides of the plane are separately ORed together with the LeCroy 64 channel OR logic unit (4564). The ORed side pairs are ANDed together resulting in four signals (S1X,S1Y,S2X,S2Y), one for each hodoscope plane. S1X and S1Y are also ORed to give S1 and similarly the S2X and S2Y gives S2. These form the 6 Hodoscope signals used in the Trigger. The above logic is drawn in Figure 2.37.
These six hodoscope signals are ECL. They are converted to NIM with Phillips 16 Channel ECL-NIM converters. The NIM signals are then delayed with manual switched delays (Phillips 792) with a range of 0 to 63.5 ns. These delay boxes are used to adjust the relative timing of the four hodoscope planes.
The NIM outputs of the 4 delay boxes are passed through ECL-NIM converters. This is to provide a fan out of ECL signals to scalers and inputs to a parallel logic unit to make coincidences of various combinations of hodoscope planes for scaling purposes.
Similarly the shower counter signals from the splitter are summed over individual planes as shown in Figure 2.39. There are 4 planes, each having 12 PMTs. They are summed in groups of 4 tubes (like the hodoscope, the signals are shuffled to avoid cross talk). Next the first two planes are summed together to give PRSUM (preradiator sum) and also all four planes are summed to give SHSUM. The PRSUM is then passed on to two NIM discriminators, one with a low threshold and the other with a high threshold. These form the PRHI and the PRLO, respectively. The SHSUM is similarly passed through a discriminator set low to give SHLO. These three signals form the shower counter part of the trigger. The electron trigger logic is shown in Figure 2.40.
The NIM outputs for the four hodoscope planes from the ECL-NIM units are used as inputs to LeCroy 365AL logic units. These units allow for the blocking of inputs without removing cables and for the setting of coincidence conditions such as 3/4. The output width on this unit may be adjusted for appropriate overlap with the other spectrometer. This module also has a single veto which can be used for coincidences or anti coincidences with a Cerenkov signal. The other inputs to this logic unit are three signals from the shower counter (PRLO, PRHI, and SHLO).
In this Logic unit S1 is ANDed with S2 to give the scintillator time of flight signal STOF, while the remaining four scintillator signals S1X, S2X, S1Y and S2Y are ANDed together with a coincidence level of 3/4 generating the SCIN signal. Next the STOF and SCIN signals are ANDed with PRLO (one of the shower counter signals) with a coincidence level of 2/3, this is vetoed by the anti Cerenkov signal to give ELLO (electron low). Similarly, the SCIN ANDed with PRHI and SHLO from the shower counter give ELHI (electron high). These two (ELLO and ELHI) are then ORed to generate the ELREAL (electron real). The SCIN is also vetoed by the Cerenkov to give the PION trigger. See Figure 2.42.
The PION trigger is prescaled as desired using a prescaling circuit which is essentially two gate generators in a loop. The ratio of the widths of these two gate generators determines the scaling factor. The prescaled pion trigger forms PIPRE. Now, the ELREAL and the PIPRE are ORed to generate the pretrigger PRETRIG.
The ELREAL is also fanned out to a bunch of diagnostic scalars to determine double pulsing rates. Both spectrometers will have all of the above components. But depending on experiment and the particles being observed some of the components need not be used.
The output of the 365AL for each spectrometer is converted to ECL for input into a LeCroy 8LM programmable logic matrix. The busy output from the JLab Trigger Supervisor is the third input into the 8LM. The 8LM, in parallel, makes the coincidence signal, singles HMS, and singles SOS. Each of this signals is generated both with and without busy for a total of 6 outputs. The three outputs with the busy veto are the inputs to the Trigger Supervisor. The trigger supervisor can be programmed to accept any desired prescale fraction of the singles triggers. The unbusy outputs are counted with scalers to measure dead time and are also used as TDC inputs.
The Trigger Supervisor has gate outputs that must be converted to NIM and anded with Original Trigger Supervisor inputs to establish the precise starts for TDC's. These logic will also generate gates of the appropriate width for the ADC's.
The individual hodoscope PMT discriminator outputs are delayed and fed into TDC's started by the focal plane trigger for the spectrometer that they are contained in. However, a number of higher level signals are sent (hodoscope OR's, focal plane triggers.) to TDC's started by the other spectrometer to measure the coincidence timing.
Currently all gate widths in the Trigger logic are set at 30 nsec.