The TOF TRIGGER makes use of two layers, connected by 72, 60 m long, cables.
The layer 1 is made of 72 LTM boards. Each board receives 48 LVDS signals, each
of them is the OR of 48 pads ( half strip). In cosmic and pp mode, the 48 signals
are OR-ed by the LTM so that each LTM sends 24 signals to the CTTM. Each bit is the OR
of 2 half-strips = ( 50 x 20 ) cm2. In addition each LTM sends to the CTTM a 25-th bit,
containing the clock used to latch the other bits, delayed of 10 ns with an internal PLL.
In the second layer the CTTM gets 1728 bits (pp and cosmic mode). The first flip-flop is latched
by the clock contained in the bit 25 of the cable. The 10 ns shift ensures the data is stable when at the
clock edge. The output of the flip flop is sent to a second flip-flop, latched by the board clock ( AliClk ).
This second chain of flip-flop is enabled by the negate of the blocking process output.
Each CTTM input channel is controlled by the blocking process. A scaler countinousosly counts the rate, with a 1 s
refresh. Ten bits are stored in a shift register to inspect for anomalies.
The blocking process output is set high when one of the following condition is satisfied:

• The channel rate is higher than a given value ( at the moment set to 400 Hz = 4 Hz/pad);
  
• The 10 bit shift register shows a string "111111111", meaning the receiver is in pull-up;
  
• The bit is flagged as "cross talk" channel ( this happens for 1 over 1728 bits);
  
• The bit is flagged as noisy channel (from LTM);
  

After a successful loading, the bits are handled by the different processes used by the CTTM to
deliver triggers. GlobalMult bits are counted in LUTs.

-- EugenioScapparone - 16 Sep 2008