1. Global Trigger Finds Correct BX
Assume we have a set of halo event from beam bunch We will see a CSC pulse peak at
a fixed offset to the beam clock edge in each chamber. This offset for the pulse beam to beam
clock edge remains constant for all halos from this bunch. Bx
Pulse Peak
SCA Sampling
BX number
Global Trigger Finds Correct BX
In the first case assume the L1A Global Trigger finds the correct beam crossing number 900. The
CFEB will calculate the L1A phase bit as 1 since it is in the second half of the SCA sample.
The CFEB will choose capacitors to store starting at Bx 889.
Pulse Peak Bx
SCA Sampling
BX number
SCA Start L1A
Pulse Peak Time

2. Global Trigger Finds Wrong BX
In the second case assume the L1A Global Trigger finds the wrong beam crossing number 901. The
CFEB will calculate the L1A phase bit as 0 since it is in the first half of the SCA sample.
The CFEB will choose capacitors to store starting at Bx 901. The pulse peak time will shift by
50 nsec.
Pulse Peak Bx
SCA Sampling
BX number
SCA Start L1A
Pulse Peak Time