I have a multi-drop RS485 arrangement with 2 slaves (HMI running on Windows XP with Modbus Slave app) and a master (Modbus Poll). I use RS232/RS485 converter in the slaves and USB/RS485 converter in the master PC. As long as both slave applications are running, the communication is ok. When one slave app is stopped, I get CRC Error in Modbus Poll master. When I remove the RS232 from the 'stopped' slave, the comms is ok again. Any ideas why I get the 'CRC Error'?