MVI56-DH485R
♦
ControlLogix Platform
Reference
DH485 Interface Module for Remote Chassis
User Manual
Page 60 of 97
ProSoft Technology, Inc.
August 27, 2009
Read Block
These blocks of data transfer information from the module to the ControlLogix
processor. The structure of the input image used to transfer data from the
module’s database to the processor is shown in the following table.
Offset Description
Length
0
Write Block ID (1 to 100)
1
1 to 40
Read Data
40
41
Read Block ID (1 to 100)
1
The Block Identification Code (word 41) is used to signal to the ControlLogix
processor that a new block is ready for processing and informs the processor of
the contents of the block. If the value of the code is set to 1, the block contains
the first 40 words of data contained in the database of the module.
The block also contains the block identification code the module expects to
receive from the processor (word 0 in the block). Under normal data transfer
conditions, the ladder logic should use the code to build the appropriate block for
the module in the output image.
In addition to the transfer of data from the module’s database to the processor,
the module also transfers status data to the processor. This is performed using
blocks with read block identification codes of -1 and 0. The format block -1 status
data is as follows:
Offset Description
Length
0
Write Block ID
1
1 to 20
Port 0 Status
20
21 to 40
Port 1 Status
20
41
Read Block ID -1
1
The block format for the 0 status data block is as follows:
Offset Description
Length
0
Write Block ID
1
1
Program Scan Counter
1
2 to 3
Product Code
2
4 to 5
Product Version
2
6 to 7
Operating System
2
8 to 9
Run Number
2
10 to 15
Data Transfer Status
6
16 to 40
Spare
25
41
Read Block ID 0
1
Ladder logic should be written to store these data sets into controller tags to
monitor the "health" of the module. Refer to the Reference chapter for a detailed
listing of the content of these data blocks.
