ATLASpix is a series of monolithic High Voltage CMOS (HVCMOS) sensor chips that are engineered to meet the requirements of outer layers of ATLAS ITk pixel tracker for HL-LHC upgrade. They are large collection electrode designs on high resistive wafers to ensure high detection efficiency and radiation tolerance. The readout electronics are placed on the chip periphery. ATLASpix1_M2 prototype is fabricated in a commercial 180 nm CMOS technology and has an active area of 1.6 cm × 0.33 cm. No clock signals are propagated inside the pixel matrix reducing the crosstalk and helping to achieve an estimated power consumption of 300 mW/cm$^2$. This work presents the design of ATLASpix_M2 with emphasis on its readout electronics, together with some experimental results.