The ABB EI812F with part number 3BDH000021R1 is a rack-mounted legacy Ethernet communication module customized for the ABB Freelance AC 800F distributed control system, serving as a complement to EI802F and EI811F modules in the same product line. Different from the RJ45-based EI811F, this module adopts a BNC interface for 10Base2 thin coaxial Ethernet connection, complying with IEEE 802.3 early Ethernet standards for legacy bus-type network topologies widely used in old industrial workshops. It obtains operating power entirely from the AC 800F backplane bus without external DC power supply, simplifying cabinet wiring and avoiding loose power connection failures under long-term mechanical vibration. Two integrated LED indicators independently display module power status and Ethernet link activity, allowing field engineers to check network faults including signal attenuation, bus terminal mismatch and link breakage without Freelance configuration software. Built with full metal shielding housing, it meets IEC 61000-6-2 industrial EMC standards, resisting strong electromagnetic interference from on-site frequency converters and high-voltage distribution equipment. Its stable operating temperature ranges from 0°C to 55°C, and storage temperature covers -20°C to 70°C, with IP20 protection grade for indoor cabinet installation. It supports limited hot swapping during system non-critical operation, which prevents overall DCS shutdown for module replacement. It is fully compatible with Freelance Control Builder software, supporting automatic hardware identification and TCP/IP parameter offline configuration. Manufactured in Sweden, each module undergoes surge and ESD testing before delivery. Though gradually phased out for RJ45 modules, it remains essential for maintaining existing 10Base2 coaxial bus networks in power, petrochemical and municipal water treatment legacy DCS projects.