Yes, a physical gateway with hardwired ethernet and RS485. There are WiFi versions available. The gateway firmware converts Modbus-TCP to/from Modbus-RTU, so the serial slave “looks like” a TCP slave to openHAB.
Actually I’ve several such gateways scattered around a large warehouse building, each serving two or three modbus devices.
This example is the exact opposite of what you’re trying to do, but the rule technique building a register from bits might be of use.
