NP5 Modbus RTU Online Manual

Setting slave address and baud rate

Slave address, baud rate and parity are dependent on the position of a virtual rotary switch and, if applicable, on objects 2028h MODBUS Slave Address, 202Ah MODBUS RTU Baudrate and 202Dh MODBUS RTU Parity. The position of the virtual rotary switch is dependent on the analog value at input ADC_ANALOG_2 (see Pin assignment).

Described in the following table is how the position of the virtual rotary switch is composed of the analog value applied at ADC_ANALOG_2 and the voltage divider:

Position of the virtual rotary switch

Upper limit digit

Formula for the voltage divider calculation

0 64
1 128
2 192
3 256
4 320
5 384
6 448
7 512
8 576
9 640
10 704
11 768
12 832
13 896
14 960
15 1023
Note: Observe the following for your voltage divider calculation:
  • If you do not want to use the analog input for setting the address, connect the ADC_ANALOG_2 pin to earth.
  • The table shows suggestions for the ratio of the voltage divider; the concrete values of all resistors are to be calculated.
  • U_REF_ANALOG is the reference voltage for the analog input, 3.3 V, see Pin assignment.
  • The current consumption of the voltage divider must not exceed 1 mA.

Described in the following is how you define the slave address, baud rate and parity via the virtual rotary switch.

Position of the virtual rotary switch

Slave address Baud rate and parity
0 Object 2028hh Object 202Ah or 202Dh
1 … 14 Number of the rotary switch Object 202Ah or 202Dh
15 5 19200, even Parity

Proceed as follows to define the position of the virtual rotary switch.

  1. Calculate the resistances for your voltage divider. You can find an example in the circuit diagram in chapter Connecting Modbus RTU. The reference voltage U_REF_ANALOG (pin B2, see Pin assignment) is 3.3 V DC.
  2. Wire input ADC_ANALOG_2 to the voltage divider.
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