Modbus Control; N159 - YASKAWA V7 Technical Manual

5.14 MODBUS CONTROL

The Drive can perform serial communication by using a programmable controller (PLC) and
®
MODBUS protocol. Modbus is composed of one master PLC and 1 to 31 (maximum) slave units
(Drives). In serial communication between the master and slaves, the master always starts
transmission and the slaves respond to it.
The master communicates with one slave at a time. Address numbers are assigned to each slave in
advance, and the master specifies an address to communicate with. The slave which receives the
command from the master executes the function, and then responds to the master.
A. Communication Specifications
• Interface
• Synchronization
• Transmission parameters
• Protocol
• Maximum number to units
to be connected
B. Setting up the Modbus
Terminals S+, S-, R+, and R- are used for modbus communications. A terminating resistor can be
enabled between R+ and R- by setting SW2 (1) to "on." SW2 is found just above the upper row of
control circuit terminals. SW2 consists of two separate switches, the switch towards the top (labeled
"1") turns on and off the terminating resistor.
The terminating resistor should only be enabled on the drive farthest away from the master.
RS-422
S+
S–
R+
R–
TERMINAL RESISTOR (1/2W, 120Ω)
: RS-485 & RS-422
: Asynchronous
: Baud rate
Data length
Parity
Stop bit
: Modbus
: 31 units
SW2
SW2
TERMINAL RESISTOR (1/2W, 120Ω)
SW1
PNP
NPN
5-16
— Selectable from 2400, 4800,
9600, 19,200 BPS (n154)
— Fixed to 8 bits
— Parity / no parity, even / odd
selectable (n155 )
— Fixed to 1 bit
RS-485
S+
S–
R+
SW2
R–
SW2
OFF ON
V I
SW2