The data from a PMT tube, called a PMT bundle, consists of three bit packed long words which can be viewed in the figure below. This data is recorded by the front end electronics (Bipolar/CMOS chips) and is eventually moved to the onboard memory via the sequencer where it can be accessed by the DAQ. The first word contains the lower 16 bits of the global trigger identifier (GT ID). The next 14 bits are the FEC channel, board and crate addresses recording where the data originated from. The remaining two bits are the CGT24 SYNCLEAR16 and SYNCLEAR24 error flags. The second word contains the 12 bit digitized analog voltages from the low gain (QLX) and high gain, short time (QHS) integrators. Packed in between is the address of the CMOS storage cell in which the PMT data was stored. The upper bits are various error/status flags from the CMOS chip. The Miss Count Flag signals that the 16 cells of the CMOS chip are full and that new data is being ignored. The LGISELECT flag indicates the state of the low gain measurement, which is set to either short (=0) or long (=1) time integrate. The last bit is the CMOS SYNCLEAR16 error flag. The third word consists of the digitized voltages from the high gain, long time integrator (QHL) and the TAC time. The remaining bits are the upper eight bits of the global trigger identifier that is recorded by the CGT24 chip.
The structure of the three words reflects the order in which the present sequencer moves the data from the front end to memory. The reader should be warned that this ordering might change with future reprogramming of the sequencer.
