Draft 0.01

                EMC Trigger Processors to Level 3 Trigger

                         Interface Specification

                            August 8, 1997



The Trigger Processor Boards (TPB) in the Level 1 EMC Trigger generate
energy sums over different regions of the calorimeter and bit maps to
give some indication of the theta positions of the energy. In addition,
summary maps of energy above various thresholds, some of which are also in
restricted theta regions of the calorimeter, are created. All data are sent
for multiple time samples. These data are read into the single EMC Trigger
ROM and zero-suppressed before being sent to OEP and hence the Level 3
trigger.



Data content to be transmitted
------------------------------

Energy sums, all for 1/40 of the EMC in phi. Each "phi sector" therefore
covers three crystals in phi in the barrel and between two and three in
the endcap. The energies are stored as 16-bit words and the sample speed
is the 3.7 MHz clock.
   Phi sum - sum over all seven towers in a phi sector.
   X sum - value of endcap tower sum in a phi sector.
   Y sum - sum over last two towers in backward direction in a phi sector.
The phi sums will be stored for 16 samples (~4.4us) and the X and Y sums
for 6 samples (~1.5us) around the L1A time.

Theta bit maps. These are also given for each phi sector and give some
indication of where most of the energy was deposited. Each phi sector
has an 8-bit map, with one bit per tower sum in theta. The exact meaning
of the bits is to be decided, but will allow the phi sum energy (above)
to be roughly positioned in theta. The maps have the same 3.7 MHz sample
speed as the energies and will be stored for the same 6 samples as the
X and Y sums.

Summary maps. These maps give the phi positions of clusters above different
configurable thresholds, with a single bit per phi position. The maps are
updated at the 7.4 MHz clock and will be stored for 12 samples (~1.5us) around
the L1A time.
   M map - clusters above ~120 MeV, in a 20-bin phi map.
   G map - clusters above ~160 MeV, in a 20-bin phi map.
   E map - clusters above ~500 MeV, in a 20-bin phi map.
   X map - clusters above ~120 MeV in the endcap only, in a 20-bin phi map.
   Y map - clusters above ~1 GeV in the backward two towers only, in a
           10-bin phi map.

There may be other data recorded for internal EMC trigger checks which are
not relevant to the L3 trigger.

These data will be zero-suppressed for speeding up subsequent data transmission
and will probably require uncompressing before use.

All lengths of the stored samples are configurable and may change with time.
The sysclk time of each of the samples will therefore be calculable from the
configuration data used for each run.