  As part of its HL-LHC upgrade program, CMS is developing a High Granularity
Calorimeter (HGCAL) to replace the existing endcap calorimeters. The HGCAL will
be realised as a sampling calorimeter, including an electromagnetic compartment
comprising 28 layers of silicon pad detectors with pad areas of 0.5 - 1.0 cm2
interspersed with absorbers. Prototype modules, based on 6-inch hexagonal
silicon pad sensors with 128 channels, have been constructed and include many
of the features required for this challenging detector. In 2016, beam tests of
sampling configurations made from these modules have been conducted both at
FNAL and at CERN using the Skiroc2 front- end chip (designed for the CALICE
experiment for ILC). In 2017, the setup has been extended with CALICEs AHCAL
prototype, a scinitillator based sampling calorimeter, and it was further
tested in dedicated beam tests at CERN. There, the new Skiroc2-CMS front-end
ASIC was used for the first time. We highlight final results from our studies
in 2016, including position resolution as well as precision
timing-measurements. Furthermore, the extended setup in 2017 is discussed and
first results from beam tests with electrons and pions are shown.
