18
Modbus RTU
This chapter describes how the individual registers, inputs, etc. are approached.
No reference is made here to addresses of the respective inputs and outputs. Addresses are to be taken
from the type-specific device datasheet in question.
Analog values
Analog values are generally treated as WORD (16 BIT) in the FB-II fieldbus system.
Temperature measurement data are forwarded as integer with 1 ⁄ 10 °C increments.
21,3 °C ............. corresponds to the value 213.
Active measurement and output values (0 .. 10 V and 0 ... 20 mA) are forwarded at a resolution of 1 ⁄ 100 of a unit.
6,7 V .................. corresponds to the value 670.
11,25 mA ......... corresponds to the value 1125.
These registers can be read respectively written using the following commands:
Measurement data ..........read Holding Registerr ............. 0x03
Output values ....................read Holding Register ............... 0x03
write Single Register................. 0x06
write Multiple Register ............. 0x17
Digital input
Digital inputs are treated as individual bits in the FB-II fieldbus system.
Here it is immaterial whether only one or several inputs are read at the same time.
Digital input .......................read Discrete Inputs ................. 0x02
Digital output
Digital outputs are treated as individual bits in the FB-II fieldbus system.
Here it is immaterial whether only one or several outputs are written or read at the same time.
Digital output ....................write Single Coil ......................... 0x05
write Multiple Coil ...................... 0x0F
read Coils .................................... 0x01
Emergency operation switches
Switches of the emergency operation level are treated as individual bits in the FB-II fieldbus system like digital inputs.
Here it is immaterial whether only one or several switches are read at the same time.
Switch ................................read Discrete Inputs ................. 0x02
Emergency operation potentiometers
Potentiometers of the emergency operation level are treated like active analog inputs in the FB-II fieldbus system.
The potentiometer position corresponds to an output signal of the respective device type (0 .. 10 V)
and is forwarded at a resolution of 1 ⁄ 100 of a unit.
U-type ...... 67% ........ corresponds to the value 670 or 6,7V respectively.
I-type ....... 50% ........ corresponds to the value 1000 or 10 mA respectively.
These registers can be read either individually or several at the same time using the following commands:
Potentiometer ..................read Holding Register ............... 0x03
