Ladder Logic
MVI56-DH485R
♦
ControlLogix Platform
User Manual
DH485 Interface Module for Remote Chassis
ProSoft Technology, Inc.
Page 37 of 97
August 27, 2009
Name Data
Type
Description
Bad_Cntl
SINT
Bad control packets
CRC_err
SINT
Packets rec with a bad CRC value
Parity_err SINT
Parity
errors
Frame_err SINT
Framing
errors
Overrun_err SINT
Overrun
errors
Unexp_err
SINT
Unexpected bytes received
Bad_LSAP_rx
SINT
Bad LSAP’s received
Refer to MVI56-DH485R Status Data (page 81) for a complete list of the data
stored in this object. This data is passed in blocks 0 and -1.
3.1.2 User Data Objects
These objects hold data to be transferred between the processor and the MVI56-
DH485R module and to aid in the generation of the ladder logic. The user data is
the read and write data transferred between the processor and the module as
"pages" of data up to 40 words long.
Name Data
Type
Description
ReadData
INT[600]
Data read from module
WriteData
INT[600]
Data to write to module
The read data (
ReadData
) is an array set to match the value entered in the
Read
Register Count
parameter of the DH485.CFG file. For ease of use, this array
should be dimensioned as an even increment of 40 words. This data is paged up
to 40 words at a time from the module to the processor. The ReadData task is
responsible for placing the data received into the proper position in the read data
array. Use this data for status and control in the ladder logic of the processor.
The write data (
WriteData
) is an array set to match the value entered in the
Write Register Count
parameter of the DH485.CFG file. For ease of use, this
array should be dimensioned as even increments of 40 words. This data is paged
up to 40 words at a time from the processor to the module. The WriteData task is
responsible for placing the write data into the output image for transfer to the
module. This data is passed from the processor to the module for status and
control information for use in other nodes on the network.
The DH485Backplane object is utilized by the ladder logic to store the variables
used in the backplane transfer operation. The structure of the object is shown in
the following diagram:
Name Data
Type
Description
LastRead
INT
Index of last read block
LastWrite
INT
Index of last write block
BlockIndex
INT
Computed block offset for data table
Other data objects can be added to the DH485ModuleDef object as required for
specific applications. It is recommended to only add objects or members to the
DH485ModuleDef object that relate to the module.
