Abstract: In view of problems that most serial servers only support main and sub machines but not support multiple main machines and Modbus TCP converting to Modbus RTU at present, an embedded share serial server was designed. The share serial server uses LM3S9B92 chip based on Cortex-M3 and realizes conversion function of a single-chip Ethernet to 3 serial ports. The test results show that the share serial server can send-receive data correctly with high communication rate and realizes function of converting Modbus TCP to Modbus RTU.