First level trigger of the backing calorimeter for the ZEUS experiment

First Level Trigger (FLT) of the Backing Calorimeter (BAC) for the ZEUS experiment is presented. The Backing Calorimeter was designed to measure the energy of particles which are not absorbed in Central Uranium Calorimeter and to identify muons. Its trigger system calculates the total energy (E), transverse energy (Et), two highest energy deposits measured in the detector (E1,E2) and provides the position of muons passing through the detector (muon bits).