The Tile Calorimeter (TileCal) is the hadronic calorimeter covering the central region of
the ATLAS experiment. The High-Luminosity phase of LHC, delivering five times the LHC nominal
instantaneous luminosity, is expected to start in 2029. TileCal will require new electronics to
meet the requirements of a 1 MHz trigger, higher ambient radiation, and to ensure better
performance under high pile-up conditions. Both the on- and off-detector TileCal electronics will
be replaced during the shutdown of 2026–2028. Approximately 10% of the PMTs, those reading out
the most exposed cells, will be replaced. PMT signals from every TileCal cell will be digitized
and sent directly to the back-end electronics, where the signals are reconstructed, stored, and
sent to the first level of trigger at a rate of 40 MHz. This will provide better precision of
the calorimeter signals used by the trigger system and will allow the development of more complex
trigger algorithms. The modular front-end electronics feature radiation-tolerant components and
redundant design to minimise single points of failure. The timing, control and communication
interface with the off-detector electronics is implemented with modern Field Programmable Gate
Arrays (FPGAs) and high speed fiber optic links running up to 9.6 Gb/s. The TileCal upgrade
program has included extensive R&D and test beam studies. A Demonstrator module equipped with the
new electronics but with reverse compatibility with the existing readout system was inserted in
ATLAS in 2019 for testing in actual detector conditions. The status of the various components and
the results of test-beam campaigns with the electronics prototypes will be discussed.