MVI56-DH485R
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ControlLogix Platform
Reference
DH485 Interface Module for Remote Chassis
User Manual
Page 72 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 access the CIF data area in
the module, select the 485CIF option for the Target Device in the MSG
instruction. The following is an example rung that displays a CIF 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 reads 10 words of data from the CIF data file in the module starting
at byte offset 0 in node 2 and places the response data in the data file N10:0 to
9. Note that the Data Table Offset value is a byte offset and not a word offset.
The size of data read is determined by the number of elements times the size of
each element. For a N-type file, the size is 1 word (2 bytes). For a F-type file, the
size is 2 words (4 bytes).
