VFD68 Variable Frequency Drives
92
Communication Specification
Outline
The Modbus protocol performs serial communication between the master and slave (VFD) using the dedicated
message frame. The dedicated message frame has functions that can read and write data. Using these
functions, you can:
•
read and write the parameter values from the VFD
•
write the input commend of the VFD
•
check the operating status
The master communicates with the slave (VFD) by accessing the assigned holding register address.
Note:
There are two different serial transmission modes: ASCII (American Standard Code for Information
Interchange) and RTU (Remote Terminal Unit) mode. This product supports only the RTU mode, in
which 1-byte (8-bit) data is transmitted as it is. Only the communication protocol is defined by the
Modbus protocol - the physical layer is not stipulated.
Table 87: Communication Specification
Item
Description
Related
Parameter
Communication Protocol
Modbus RTU protocol
P.549
Conforming Standard
EIA-485 (RS-485)
—
Number of Connectable Devices
1:N (maximum 32 units), setting is 0 to 247 stations
P.117
Communication Speed
Select 4800, 9600, 19200, or 38400 bps
P.118
Control Procedure
Asynchronous
—
Communication Method
Half-duplex
—
Communication
Character System
Binary (always 8 bits)
—
Start Bit
1 bit
—
Stop Bit Length
•
No parity, stop bit length: 2 bits
•
Odd Parity; stop bit length: 1 bit
•
Even parity; stop bit length: 1 bit
P.120
Parity Check
Error Check
CRC code check
—
Terminator
Not used
—
Waiting Time Setting
Not used
—
