SystemAir HHFlex C, Operating Instructions Manual, Page: 42 / 47

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7 BUS COMMUNICATION
7.1 General
The HHFlex controller is capable of communicating via RS485(Modbus) and TCP/IP(BACnet/IP)
7.2 Modbus
Modbus communication takes place via RS485 (port 2, main controller) or via IP (IP port, main controller).
7.2.1 Communication Settings
The Modbus communication settings can be configured in the web panel in the Settings menu or with the external display unit under
Settings => Modbus Config
Adress (0-255)
Baudrate (300, 600, 1200, 2400, 4800, 9600, 14400 or 19200)
Parity (None, Odd or Even)
Stop bits 1 (not configurable)
7.2.2 Modbus type
The Modbus types of the signals:
1 = Coil Status Register (Modbus function = 1, 5
and 15)
2 = Input Status Register (Modbus function = 2)
3 = Holding Register (Modbus function = 3, 6 and 16)
4 = Input Register (Modbus function = 4)
2 and 4 are read-only , while 1 and 3 are read-write .
7.2.3 Modbus functions
The Modbus master uses different Modbus functions in its query, depending on whether to read or write values. A function also
describes what signal type it is meant for.
Supported Modbus functions:
1 = Read Coils
2 = Read Discrete Input
3 = Read Holding Register
4 = Read Input Register (Direct 16 Bit)
5 = Write Single Coil
6 = Write Single Register
15 = Write Multiple Coils
16 = Write Multiple Registers
7.2.4 Max. 47 registers
Max. 47 registers can be read in one message.
7.2.5 Communication limits
The Modbus master must wait for a minimum of 3.5 charactertimes (4 ms at 9600 bps) between two messages. When the Modbus
master communicates with more than one HHFlex controller on the same communication line (RS485), the Modbus master must
wait for a minimum of 14 charactertimes (16 ms at 9600 bps) between the answer and the first question for the next controller.
In the HHFlex controller there is a limit of 10 fast communications in every half minute, the other communications will have a
delayed answer of approximately 1 s.
7.2.6 Scale factor
Real signals have scale factor 1 except temperature signals that have scale factor 10 for Modbus communication.
Integer, Index and Logic always have scale factor 1.