  The KM2A(one kilometer square extensive air shower array) is the largest
detector array in the LHAA- SO(Large High Altitude Air Shower Observatory)
project. The KM2A consists of 5635 EDs(Electromagnetic particle Detectors) and
1221 MDs(Muon Detectors). The EDs are distributed and exposed in the wild. Two
channels, Anode and Dynode, are employed for the PMT(photomultiplier tube)
signal readout. The readout electronics proposed in this paper aims at the
accurate charge and arrival time measurement of the PMT signals, which cover a
large amplitude range from 20P.E(photoelectrons) to 2x10^5 P.E. By using the
Trigger-less architecture, we digitize signals close to the PMTs. All digitized
data is transmitted to DAQ(Data Acquisition) via the simplified WR(White
Rabbit) protocol. Compared with traditional high energy experiments,
high-precision of time measurement in such a large area and suppression of
temperature effects in the wild become the key techniques. Experiments show
that the design has fulfilled the requirements in this project.
