INS_RL1000GW_REV– 15 Jul 2016 PAGE 126
INSTALLATION AND OPERATION MANUAL
RL1000GW
TECH SUPPORT: 1.888.678.9427
Modbus Gateway
The ComNet capability of gateway Modbus RTU to Modbus TCP is of yet another benefit to
industrial area applications.
The router allows connecting an RS232 Modbus RTU and gateway it to a remote Modbus TCP
client (SCADA) over the Ethernet.
The Modbus RTU slave is connected at the router local serial port, over an RS232 link. The
Modbus TCP Client (SCADA) may be connected directly to the router Ethernet port or via an IP
cloud. The router gateway will encapsulate the Modbus RTU to a TCP packet with port 502.
The router Modbus gateway is assigned with the stations ID of the Modbus RTU devices
connected to it.
The gateway is set to use a ACE IP interface as its TCP traffic source.
Packet sent from Modbus TCP Client will carry the gateway IP interface and the Modbus RTU
station ID as its target. The gateway will listen to incoming packets and forward the message in a
serial uniform to relevant Modbus RTU using the station id as identifier.
Up to 5 instances of a gateway can co-exist. Each must use a different ACE IP interface and have a
unique gateway-id.
A serial port, connecting a Modbus RTU device, can be associated with a single gateway instance.
A Modbus RTU device must have at least one Modbus ID. Each Modbus ID must be unique
behind the gateway.
Implementation
The Modbus gateway is supported between a Modbus TCP and a Modbus RTU.
Modbus TCP gateway to Modbus ASCII is not implemented.
The gateway translates Modbus frames of same structure, meaning is it a prerequisite to have the
Modbus TCP device use the same frame structure as the Modbus RTU device.
