Solution:

485DRCi If an RS-232 to RS-485 converter, is added to a 2-wire RS-485 network in order to add an RS-232 device to an RS-485 network, the RS-232 device will see all of the RS-485 traffic that is on the RS-485 bus. If the RS-232 device has its RS-232 cable disconnected, then the RS-485 data being sent out may appear as interference data coming back into the RS-232 to RS-485 converter. This will enable the RS-485 driver chip and will halt communication to the other RS-485 devices. In this application, you may need to use RS-232 cable that has conductors that are individually shielded, and tie the shields to earth ground. This will prevent the transmitted RS-485 data, sent out the RS-232 transmit line, from being echoed onto the RS-232 receive data line.