Suntex EC-4110-I, Operation Manual

Page: 70 / 88

9. Modbus Protocol and Instructions
9.1 Communication connection
The RS-485 communication port of the transmitter EC-4110-I and EC-4110-ICON features
electronic isolation protection, lightning protection, and provides internal independent ground
solution. It is allowed to use normal twisted-pair (segregation double-stranded twisted pair
cable) cable connections. All devices are in contact with a double-stranded, and then all together,
and another line will be connected with all the negative contacts, and the isolated shield wire
must be connected to GND. When talking about communication in the laboratory, the
stand-alone master-slave communication is relatively simple. Hence, it is allowed to consider
using the normal cable instead. However, there should be strictly in accordance with the
requirements of industrial engineering construction. Wiring diagram is as follows:
Note:
1. The RS-485 interface of transmitter EC-4110-I/EC-4110-ICON has a protective earth terminal.
When it communicates with the RS-485, there should use with solution ground to eliminate risk
of safety.
2. It is allowed to use an 120 ohm impedance matching resistors at terminal equipment across both
ends of transmission lines (D +(B), D-(A)) to effectively reduce or eliminate signal reflection.
Note:
there are three possible situations resulting in failure connection:
a. Open circuits: the signal cable has open circuits.
b. Short circuits: the insulation that is insufficient between signal cables causes short circuits.
c. Idle-bus: there is no data transmission in the Controlbus.
Based on the previous three situations resulting in unknown state of Controlbus’s voltage, the
receiver accepts the unexpected signals. Therefore, in some harsh environment like
multi-transmitter connection, the Controlbus needs the terminator to avoid reflection of baud rate,
and it needs pull-high resistor, pull-low resistor, and biasing circuits made up of V
Bus
as the block
diagrams showing above. Besides, it makes sure that the free voltage between transmission line
D+(B) and D-(A) is available for maintaining the completeness of the signals. Due to not each
environment being suitable for fixed resistor and V
Bus
, as a result, users must pay attention to the
settings. Some parts of connecting instruments (as parts of RS-485 or modules) provide the
terminator, pull-high resistor, pull-low resistor, and settings of V
Bus
. Please refer to the operation
V
Bus
GND
灿 灿
D+(B)
GND Master
D-(A)
EC-4110-I
ID
烉
01
EC-4110-I
ID
烉
02
Other
Modbus
Equipment
įįįįį
灿
灿
Depending on
the actual
situation
Pull-up resistor
R
pull-high
Terminator
R
T
Pull-down
resistor
R
pull-low
по