Aport-212 User Guide
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4. Modbus Gateway Operation
Modbus gateway acts as a communication interpreter between Modbus TCP and Modbus RTU/ASCII.
When Ethernet is connected to a Master device such as a Human Machine Interface (HMI), the serial
port will be configured as a Slave RTU/ASCII to connect to Modbus slave device such as digital meter.
On the contrary, if Ethernet is connected to a Slave device such as PLC, then serial port should be
configured as a Mater RTU/ASCII.
4.1 Slave RTU / ASCII Mode
When Modbus Masters are Ethernet devices, up to 16 Master devices can access the same serial port
to communicate with the serial Slave devices. Maximum 64 Master TCP request can be buffered and
Unit ID (UID), which is used to address the serial device, can tell Aport-212 which serial port to send the
command. In figure slave RTU shown as follow data with UID 1 to 123 will go to port 1 and 124 to 247
will use port 2.
Sometimes, it is difficult to use UID as the device address, you can use address offset to provide the
flexibility. If the address offset is applied, Slave address=UID+ address offset.
4.2 Response Time Out
Time out setting is used to check if the slave responses to the Aport-
212’s Modbus command in time.
In the case of time out, Aport-212 will discard the request of Modbus TCP command and issue a TCP
exception if it is enabled.
