To address the issue of poor real-time performance and low reliability in communication between the serial interface of distributed I/O devices and external systems, a design for an IO station device based on PROFINET real-time industrial Ethernet has been proposed. A dual-core model is presented, utilizing the PROFINET communication core chip and RS485 application core chip. The PROFINET communication core chip is an application-specific integrated circuit (ASIC), while the RS485 application core chip is based on the STM32 microcontroller. The dual-core model collectively handles the conversion between the PROFINET protocol and the RS485 protocol. The process of non-cyclic and cyclic data interaction between the main station controller and IO modules through the IO station device is analyzed. A generic station description (GSD) file for the IO station device and IO modules is designed. By integrating PROFINET network communication interfaces and RS485 communication interfaces into the IO station device, a complete PROFINET IO communication test platform is established, and system configuration is completed. The test results indicate that the designed IO station device achieves cross-network communication from PROFINET to RS485, providing a feasible and reliable solution for connecting traditional distributed I/O devices to the PROFINET industrial Ethernet in the field of technology.