Oriental motor BLH Series - 11 Modbus RTU Control (RS-485 Communication); Modbus RTU Specifications

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Modbus RTU control (RS-485 communication)
11 Modbus RTU control
(RS-485 communication)
This chapter describes how to control from the host controller via RS-485 communication. The protocol used in RS-485
communication is the Modbus protocol.
11.1 Modbus RTU specications
The Modbus protocol is simple to use and its specication is open to the public, so this protocol is widely used in
industrial applications.
Modbus communication is based on the single-master/multiple-slave method. Only the master can issue a query
(command).
Each slave executes the process requested by query and returns a response message.
The
BLH
Series RS-485 communication type supports the RTU mode only as the transmission mode. The ASC
Ⅱ
mode is
not supported. Under this protocol, messages are sent in one of two methods.
z
Unicast mode
The master sends a query to only one slave. The slave executes the process
and returns a response.
Query
Response
Master
Slave
z
Broadcast mode
If slave address 0 is specied on the master, the master can send a command
to all slaves. Each slave executes the process, but does not return a response.
Master
Slave No response
Query
11.1.1 Communication specications
Electrical
characteristics
In conformance with EIA-485
Use a twisted pair cable and keep the total extension distance of the communication cable up to 10 m (32.8 ft.).
*
Communication
mode
Half duplex
Asynchronous mode (data: 8 bits, stop bit: 1 bit/2 bits, parity: none/even number/odd number)
Transmission rate Selectable from 9,600 bps, 19,200 bps, 38,400 bps, 57,600 bps, 115,200 bps, and 230,400 bps.
Protocol Modbus RTU mode
Type of
Connection
Up to 15 drivers can be connected to one programmable controller (master device).
*
If the motor cable or the power supply cable generates an undesirable amount of noise depending on the wiring or
conguration, shield the cable or install a ferrite core.

Connection diagram
CN1 CN2
+
-
CN3
CN6
CN5
C-DAT C-ERR
CN4
PWR/ALM
IDTERM.
NO
CN1 CN2
+
-
CN3
CN6
CN5
C-DAT C-ERR
CN4
PWR/ALM
IDTERM.
NO
CN1 CN2
+
-
CN3
CN6
CN5
C-DAT C-ERR
CN4
PWR/ALM
IDTERM.
NO
Host controller
Address No.1 Address No.2 Address No.15
Termination resistor
(TERM.):ON