Connecting Modbus RTU
The following figure shows a reference circuit for connecting the NP5-02 Modbus RTU via RS485.
Note: For the standard assignment of the connections, see Pin assignment.
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PCI-specific pin assignment for Modbus RTU:
|
Pin |
Name |
Description |
|---|---|---|
| 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 |
| A19 | COMM_SPI_MOSI | Receiver Enable |
| 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. |
| B22 | COMM_RESET | Driver Enable |
Tip: If you do not use the ADC_ANALOG_2 analog input to set the address and baud rate, connect pin A13 to GND.
RS-485 line polarization
Note: The controller is not equipped with line polarization and expects the master device to have one.
If the master device on the bus does not have line polarization of its own, a pair of resistors must be attached to the RS-485 balanced cables:
- 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.
