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Configuring Modbus
334 IOLAN SDS/SCS/STS/MDC User’s Guide, Version 4.0
Modbus Gateway Settings
The scenarios in this section are used to illustrate how the IOLAN’s Modbus Gateway settings are
incorporated into a Modbus device environment. Depending on how your Modbus Master or Slave
devices are distributed, the IOLAN can act as both a Slave and Master Gateway(s) on a multiport
IOLAN or as either a Slave or Master Gateway on a single port IOLAN.
Modbus Master Gateway
The IOLAN acts as a Master Gateway when the Modbus Master is connected to a serial port on the
IOLAN. Each Modbus Master can communicate to UIDs 1-247.
IOLAN
Network
EIA-232
EIA-422/485
TCP
Modbus Slave
Modbus Slave
Modbus Slave
Modbus Master
Master Gateway
Modbus Master
Serial
Modbus Slave Gateway
The IOLAN acts as a Slave Gateway when the Modbus Master resides on the TCP/Ethernet network
and the Modbus Slaves are connected to the serial ports on the IOLAN. Note: The IOLAN provides a
single gateway to the network-attached Modbus Masters. This means that all Modbus Slaves attached
to the IOLAN’s serial ports must have a unique UID. Multiple Masters on the network can
communicate with these Modbus Slaves. Note: If a transaction is in progress to a Modbus Slave,
other requests to that same device will be queued until that transaction is complete.
IOLAN
Network
EIA-232
EIA-422/485
TCP
Modbus Slave
Modbus Slave
Modbus Slave
Modbus Master
Slave Gateway
Modbus Master
Modbus Slave
Serial