CIRCUTOR DHB Series - Manual (Page 37)

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the shield only to a single point of the protection terminal).
The GND line serves to the additional protection of the interface line at
long connections. Then, one must connect GND signals of all devices
on the RS-485 bus.
To obtain the connection with the computer, a RS-485 interface card or
a suitable converter is indispensable, e.g. PD51 or PD10.
The connection way of devices is shown on the fig. 13.
The designation of transmission lines for the card in the PC computer
depends on the card producer.
6.2. Description of the MODBUS Protocol
Implementation
The implemented protocol is in accordance with the PI-MBUS-300 Rev G
of Modicon Company specification.
Set of the serial protocol parameters of DHB-124 meters in MODBUS pro-
tocol:
l
meter address 1...247,
l
baud rate 4800, 9600, 19200, 38400,
57600, 115200 bit/s,
l
work mode RTU with a frame in format 8n2, 8e1,
8o1, 8n1,
l
maximal response time 100 ms.
The parameter configuration of the serial interface consists in the settlement
of the baud rate (bAUd parameter), device address (Addr parameter),
and the format of the information unit (prot. parameter)
Notice:
Each meter connected to the communication network must have:
l
unique address, different from addresses of other devices
connected to the network,
l
identical baud rate and type of information unit.