MVI56-DH485R
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ControlLogix Platform
Reference
DH485 Interface Module for Remote Chassis
User Manual
Page 74 of 97
ProSoft Technology, Inc.
August 27, 2009
Read Access
In order to monitor data contained in the DH-485 driver module, a read command
message must be executed from the ladder logic. To read the data area in the
module, select the 500CPU option for the Target Device in the MSG instruction.
The following is an example rung that displays a data file access method MSG
instruction:
You must allocate a unique area in the SLC’s data file area for the Control Block
area used by the MSG instruction. Failure to provide this area will result in
unpredictable behavior. Select the Setup Screen area in the MSG instruction to
display the following dialog box:
This example will read 10 words from the module and place the data in the SLC
data file area N10:0 to 9. N-files are emulated on the module containing the DH-
485 driver. If the module is configured for the first N file of N7, a file size of 200
and a file offset value of 0, the module will respond with the words held in the
module’s internal database registers 200 to 209 for this command. Refer to the
DH-485 driver database documentation for a full explanation of the module’s
internal database.
