Each MBTS module is readout by a PMT, the signal is shaped and  amplified by the 
TileCal electronics and it is made available in USA15  at the TileCal trigger output. 
At this point the L1 central  trigger takes over to make out of the 32 signals  some
 L1 trigger  items.

These are the steps:

1. each signals is amplified (x2) and split into 2
2. one signal is discriminated with leading edge discriminators
3. the output of the discriminator is sent to the CTP
4. the CTP forms the side multiplicity and constructs the trigger  items (like L1_MBTS_1_1)
5. L1A is issued

The L1_MBTS_1_1 bit from the CTP and the MBTS  multiplicity formed inside the 
CTP are not available as external signals.

The second signal is meant to be used with the constant fraction  discriminators 
and to possibly count the MBTS multiplicity and apply  some logic outside the CTP. 
This is not yet in place. Once this second  path will be commissioned it will be an 
additional input to the CTP  and possibly used as a trigger input to form a L1 trigger
 item. This will not happen during the first period of  commissioning of ATLAS with beam. 
 On the other hand an external trigger signal form this path could be provided since 
it is all going to be  performed with NIM modules.