The ZDC upgraded its readout system for run3 in order to operate in continuous mode without dead time at 2.5 MHz event rate. The purpose was to preserve the run2 energy and time resolution performance in the challenging environment of run3 Pb-Pb collisions. The new acquisition chain is based on a commercial 12 bit digitizer with a sampling rate of about 1 GSps, assembled on an FPGA Mezzanine Card. The signals produced by the 26 ZDC channels are digitized and samples are processed through an FPGA in order to extract information as timing, baseline average estimation and luminosity. Thanks to the low crossing angle it was possible to include the ZDC in the global physics run during the VdM scans data taking. The ZDC was fully operational and performed the validation as luminometer.