4
IM 77J01A0E11-01E
8th Edition
5. COMMUNICATION OVERVIEW
5.1
Communication Specifications
Ethernet Specifications
Interface
Conforms to IEEE802.3 (10BASE-T/100BASE-
TX)
Port number for Modbus/TCP protocol: 502
Host devices (PC, etc.)
MODBUS/TCP
TCP
IP
Ethernet
10BASE-T/100BASE-TX
Application layer
Transport layer
Network layer
Data link layer
Physical layer
Access control CSMA/CD
Transfer rate
10 Mbps/100 Mbps
Maximum
segment length
100 m (the length between Hub and converter)
Maximum
connecting
configuration
Up to 4 cascade connections per hub
(10BASE-T), up to 2 cascade connections per
hub (100BASE-TX)
The number of
connection
1
The maximum
number of
transactions
1
Communication
parameter
settings
High-speed response mode, parity, IP address,
subnet mask, default gateway and port number
via Ethernet using the dedicated tool.
RS-485 Specifications
Interface
Conform to EIA RS-485
Protocol
Modbus/RTU
Transfer system
Half-duplex communication
S y n c h r o n o u s
system
Start-stop synchronization
Transfer rate
9600 bps
Parity
Even, odd or none
Stop bit
1 bit
Data length
8 bit
5.2 TCP/IP Communication
Modbus/TCP exchanges data with the protocol shown in the
figure below using a TCP/IP socket interface.
RS-485 connection
devices
Signal Conditioners
JUXTA series
Controllers
GREEN series
UT100 series
Power Monitors
POWERCERT series
PC
socket()
socket()
bind()
listen()
accept()
connect()
send()
send()
recv()
recv()
close()
close()
First startup
First startup
Open connection
Command
Response
Terminate connection
CAUTION
●
If no request is received from the host device
for more than 60 seconds after establishing a
connection, the VJET will automatically terminate
the connection.
●
The maximum number of VJET transactions is “1”.
When sending commands continuously, confirm the
response from VJET and send the next command.
5.3 Network Frame Structure
The Modbus/TCP frame structure is as follows:
MBAP Header
Function codes
Data
Modbus TCP/IP ADU
PDU
MBAP Header (Modbus Application Protocol Header)
Header used to identify the the Modbus/TCP protocol
PDU (Simple Protocol Data Unit)
Body of the data communication
5.3.1 MBAP Header Structure
The MBAP Header (Modbus Application Header) consists of
the following seven bytes.
Description Transaction
ID
Protocol
ID
Number of
bytes
Unit
ID
Byte No.
0
1
2
3
4
5
6
Transaction ID:
The host device specifies an arbitrary
value to identify a trasaction.
The VJET returns the value it received
from the host device as its response.
Protocol ID:
This parameter is set to “0” to indicate
the Modbus/TCP protocol.
Number of
bytes:
The number of bytes from the Unit ID
(byte number 6) byte on.
Unit ID:
Unit ID of RS-485 connection device.
5.3.2 PDU Structure
The PDU (Simple Protocol Data Unit) consists of the
following n bytes.
Description Function code
Data
Byte No.
0
1 to (n−1)
Function code:
The command specified from the host
device.
Data:
Depending on the function code, D
register addresses, the number of
individual D registers, or parameter
values are specified in this position.
5.4 List of Function Codes
The codes in the following list are command words host devices
use to acquire information from the internal registers (D registers)
of RS-485 connection devices.
Code Number
03
06
08
16
Function
Reads data from multiple registers
Writes data to registers
Loop back test
Writes data to multiple registers
For details, refer to the Communication Functions user’s
manual of each RS-485 connection device.
