What it does and where it fits
The 6GK7243-1PX30-0XE0: The module occupies one single-width slot on the S7-1200 rail (30 mm wide, 110 mm tall, 75 mm deep) and is protected to IP20. A single RJ45 port provides the Ethernet connection at 10 – 100 Mbit/s. It draws 0.25 A from the 5 V DC backplane bus (typical), dissipating 1.25 W. That power draw is stable enough to factor into the CPU's backplane budget without surprise.