MVI56-DH485R
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ControlLogix Platform
Reference
DH485 Interface Module for Remote Chassis
User Manual
Page 70 of 97
ProSoft Technology, Inc.
August 27, 2009
5.2.7 SLC Interface
The DH-485 driver is written for peer-to-peer operation on the DH-485 network.
Therefore, the driver can both execute commands (master role) and respond to
commands (slave role). If the driver contains no commands, ladder logic is
required in the other DH-485 nodes in order to control or access the data in the
module containing the driver. If the driver is configured with user defined
commands, these commands will control or monitor data in other nodes on the
network without the ladder logic requirement. The driver is developed to support
both modes of operation simultaneously.
The section first describes the SLC configuration required for the DH-485
protocol and the cabling required. Following this discussion, the section contains
example ladder logic to interface with the module’s database.
The ladder logic required in an SLC to interface with the DH-485 Driver uses the
MSG instruction. The DH-485 driver supports two data access options. You can
interface to a module containing the DH-485 driver using the CIF (Common
Interface File) or normal SLC data file access. Use of the CIF access is limited to
a data area of 244 bytes and is offered for backwards compatibility to older
processors and should be used only when the data access method is not
available. The preferred method of data access to the driver is through the use of
the SLC data files. This access method permits full access to the data contained
in the module’s internal database.
SLC Communication Set Up
In order to use the DH-485 port on the SLC, channel 0 or 1 must be configured
as a DH-485 port. Select Channel Configuration from the RSLogix 500 software
to display the following dialog box.
