Modbus. Rosemount Smart Wireless Gateway

Section 5: Host Integration

January 2015

5.4

5.4.1

Reference Manual

00809-0200-4420, Rev HB

Modbus

The Gateway supports both Modbus RTU over the RS-485 serial port and Modbus TCP over

Ethernet. It functions as a sub device on the Modbus network and must be polled by a Modbus master or client (host system).

Communication settings

It is import that the Modbus communication settings in the Gateway match the setting in the

Modbus master or client. Please refer to host system documentation for more information on how to configure these settings. The Modbus communication settings can be found by navigating to System Settings>Protocols>Modbus.

Figure 5-5. Modbus Communications Page

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One Modbus Address: When this option is selected, this address is used by the Gateway for

Modbus RTU communications.

Multiple Modbus Addresses: When this option is selected, a new column for address will appear on the Modbus mapping page.

Modbus TCP Port: This is the TCP/IP port the Gateway uses for Modbus TCP (Ethernet). To change TCP/IP port settings, see the Internal Firewall section for more details.

Host Integration

Reference Manual

00809-0200-4420, Rev HB

Section 5: Host Integration

January 2015

Host Integration

Baud Rate: The data rate or speed of serial communications. This setting is only required for

Modbus RTU.

Parity: This setting determines parity (none, even, or odd) to use for error checking purposes.

This setting is only required for Modbus RTU.

Stop Bits: This setting determines the number (1 or 2) of stop bits to use when ending a message. This setting is only required for Modbus RTU.

Response delay time (ms): This setting determines how long (ms) the Gateway waits before responding to a Modbus request. This setting is only required for Modbus RTU.

Unmapped register read response?: This is the value returned by the Gateway if the Modbus master requests a register with no data assigned to it (empty register). It is recommended this be set to zero fill to prevent errors.

Floating point representation: This setting determines if the Gateway uses floating point values or integer values. There are three options for this setting.

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Float uses 32 bit floating point values.

Round rounds the data value to the nearest whole number.

Scaled uses scaled integers to offset negative values or increase decimal point resolution. The equation for scaled integers is: y = Ax - (B - 32768)

Where: y = Scaled integer returned by the Gateway

A = Gain for scaled integer value x = Measured value from wireless field device

B = Offset for scaled integer value

Use swapped floating point format?: This setting switches which register is sent first for a floating point value. This setting is only used for floating point values.

Incorporate value’s associated status as error?: This setting will cause the Gateway to report a predetermined value when a communications or critical diagnostic error is received from the wireless field device. The value is user configurable depending on which floating point representation is chosen. See Value reported for error below.

Value reported for error (floating point): This setting determines what value is reported if the wireless field device reports a failure or stops communicating to the Gateway. This setting is used for floating point values. The choices are NaN (not a number), +Inf (positive infinity), -Inf

(negative infinity), or Other (user specified).

Value reported for error (rounded and native integer): This setting determines what value is reported if the wireless field device reports a failure or stops communicating to the Gateway.

This setting is used for rounded or scaled integers. The choice is a user specified value between

-32768 and 65535.

Scaled floating point maximum integer value: This determines the maximum integer value for the purpose scaling integers. 999-65534

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