Results from the completed Phase 1 Upgrade of the Compact Muon Solenoid (CMS)
Level-1 Calorimeter Trigger are presented. The upgrade was performed in two stages, with the first
running in 2015 for proton and heavy ion collisions and the final stage for 2016 data taking. The
Level-1 trigger has been fully commissioned and has been used by CMS to collect over 43 fb−1 of
data since the start of the Run II of the Large Hadron Collider (LHC). The new trigger has been
designed to improve the performance at high luminosity and large number of simultaneous inelastic
collisions per crossing (pile-up). For this purpose it uses a novel design, the Time Multiplexed
Trigger (TMT), which enables the data from an event to be processed by a single trigger processor
at full granularity over several bunch crossings. The TMT design is a modular design based on
the µTCA standard. The trigger processors are instrumented with Xilinx Virtex-7 690 FPGAs and
10 Gbps optical links. The TMT architecture is flexible and the number of trigger processors can
be expanded according to the physics needs of CMS. Sophisticated and innovative algorithms are
now the core of the first decision layer of the experiment. The system has been able to adapt to
the outstanding performance of the LHC, which ran with an instantaneous luminosity well above
design. The performance of the system for single physics objects are presented along with the
optimizations foreseen to maintain the thresholds for the harsher conditions expected during the
LHC Run II and Run III periods.