Hardware reference guide

Modbus Plus NOMs
35013379 02 October 2007 287
Front Panel
Switches
Two, three-position slide switches are located on the front of the unit. The three-
position slide switch on the right is used to select the comm parameter settings for
the Modbus (RS-232) port provided with the Modbus Plus option module. Three
options are available, as shown in the following illustration.
Setting the slide switch to the top position assigns ASCII functionality to the port. The
following comm parameters are set and cannot be changed.
Setting the slide switch to the middle position assigns remote terminal unit (RTU)
functionality to the port; the following comm parameters are set and cannot be
changed.
Note: If the left-hand switch is in the upper position and right-hand switch is set to
mem then, as of firmware version 2.20, bridge mode is deactivated. This means
that the network connection between Modbus and Modbus Plus is locked.
The NOM hardware defaults to bridge mode when the front panel switch is set to
RTU or ASCII mode. When networking controllers, a panel device connected to the
NOM Modbus port can communicate with the controller to which it is conected, as
well as log into any nodes on the Modbus Plus network.
ASCII Comm Port Parameters
Baud 2,400
Parity Even
Data Bits 7
Stop Bits 1
Device Address Rear panel rotary switch setting
RTU Comm Port Parameters
Baud 9,600
Parity Even
Data Bits 8
Stop Bits 1
Device Address Rear panel rotary switch setting
ASCII
RTU
mem
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com