User's Manual

Page 42 E2 Wireless I/O
4.6 Serial Configuration
The E2 has an RS-232, and RS-485 port for serial communications. These ports may
be used to connect external Modbus RTU devices via the Modbus TCP to RTU
Gateway.
Modbus TCP to RTU Gateway
The Modbus TCP to RTU Gateway allows an Ethernet Modbus/TCP Client (Master) to
communicate with a serial Modbus RTU Slave. The E2 makes this possible by internally
performing the necessary protocol conversion. The conversion is always performed by
the E2, which is directly connected to the Modbus serial device (i.e. only this module
needs to have Modbus TCP to RTU Gateway enabled).
The example below demonstrates how a Modbus/TCP Client (Master) can connect to
one or more Modbus RTU (i.e serial) Slaves. In this example the E2 Access Point is
configured with the “RS232 Modbus/TCP to RTU Gateway” enabled.
Once enabled, the gateway converts the Modbus/TCP queries received from the
Master into Modbus RTU queries and forwards these over the RS232 port to the Slave.
When the serial response to the query arrives from the Slave, it is converted to a
Modbus/TCP response and forwarded via the network to the Modbus/TCP Master. If no
response was received serially by the E2 within the configured Response Timeout, the
E2 will initiate a number of retries specified by the configured Maximum Request
Retries.
The Modbus TCP to RTU Gateway may be configured to operate on either the RS-232
or RS-485 port.
D1 D2 D3 D4 D5 D6 D7 D8
AI 1 AI2
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AO1 AO2
COM+24V+-+- COM+24V++
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AI 1 AI2
AI3 AI4
AO1 AO2
COM+24V+-+- COM+24V++