Modbus: Modbus communication failures summary.

1. The device is not energized.
2. A communication protocol is the same (host 485 is a slave RS485);
1. Communication line reversed;
2. right serial port parameters: baud rate, data length, parity, stop bits;
3.modbus ID right;
4. modbus RTC (CRC) check right;
5.modbus function code is not supported;
6.modbus read address does not exist;