RS-485

An RS-485 port (J5) is provided on UART1 for the testing of custom drivers to be written by a developer. Table 4 provides RS-485 connector pinouts.

Table 4. RS-485 port pinouts

Pin Signal
1 RS-485 Signal B (-)
2 RS-485 Signal A (+)
3 Reference Ground (S)



To drive the RS-485 interface, UART1 must be used in 2-wire mode, and DIO17 and DIO18 are used to control the enable signals on the RS-485 device. Table 5 shows the functions provided:

Table 5. DIO18 (DE) and DIO17 (REN) functions for RS-485 interface

DIO18 (DE) DIO17 (REN) Function
0 0 Rx Mode
0 1 Shutdown. Use this mode to save current when the module sleeps.
1 0 Do not use.
1 1 Tx Mode

If the RS-485 interface is not required, then all four signals can be disconnected from the RS-485 by removing resistors R28, R29, R32 and R34. This allows the signals to be used on expansion header J4.