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Modbus communications – Rockwell Automation 1405-M620 Operating Instructions User Manual

Page 11

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Publication 1405-IN002C-EN-P - November 2004

Bulletin 1405 (M620) Operating Instructions 11

Modbus Communications

The M620 is available with an RS-485 half-duplex communications
port which supports Modbus RTU slave protocol version 1.0. The
following Modbus commands are supported:

03 (0x03) Read Holding Registers

16 (0x10) Write Multiple Registers

43 (0x2B) Read Device Identification

The port may be configured during instrument setup. The baud rate
may be set to 9.6 K or 19.2 K bits per second. The Modbus address
may be set in the range 1 to 257.

The M620 equipped with Modbus includes 2 LEDs which display
Modbus status and Network status.

Modbus Port Connections

Connections to the Modbus port are made via a 3-pin connector as
shown below:

1

2

3

Rx Tx-

Grd

Rx Tx+

Terminating resistors are not included in the M620. If
needed, terminating resistors must be provided and
installed by the user.

Modbus Memory Map

The tables below provide a cross-reference of Modbus register
address to metered value along with data type.

IMPORTANT