Support M487 board

Dependencies:   Modbus nvt_rs485

History

1. Support M487 board.; 2. Disable get value from Dip switch, if def-rs485-port value is 1 in mbed_app.json file. default tip

2017-10-06, by wclin [Fri, 06 Oct 2017 02:28:18 +0000] rev 0

1. Support M487 board.; 2. Disable get value from Dip switch, if def-rs485-port value is 1 in mbed_app.json file.