Connecting Modbus RTU
The following figure shows a reference circuit for connecting the NP5-02 Modbus RTU via RS485.
PCI-specific pin assignment for Modbus RTU:
|A13||ADC_ANALOG_2||The slave address is defined via the applied voltage, see Setting slave address and baud rate|
|A16||SLOT_SPI_MISO||Modbus RX Data|
|A17||SLOT_SPI_SCK||Modbus TX Data|
|B2||U_REF_ANALOG||Is used as a reference voltage of 3.3 V DC to define the slave address, see Setting slave address and baud rate|
RS-485 line polarization
- A pull-up resistor to a 5V voltage on the RS-485+ (D1) cable
- A pull-down resistor to earth (GND) on the RS-485- (D0) cable
In this case, a line polarization must be attached at a location for the entire serial bus. In general, this location should be on the master device or its connection. All other devices then no longer need to implement line polarization.