ProSoft Technology MVI56E-MNETCR - Manual (Page 100)

Reference MVI56E-MNETCR ♦ ControlLogix Platform
User Manual Modbus TCP/IP Multi Client Enhanced Communications Module for Remote Chassis
Page 100 of 159 ProSoft Technology, Inc.
June 14, 2011
Normal Data Transfers
Normal data transfer includes the paging of the user data and status data found
in the module’s internal database in registers 0 to 4999. These data are
transferred through read (input image) and write (output image) blocks. The
following topics describe the function and structure of each block.
Block Response from Module to Processor
These blocks of data transfer information from the module to the ControlLogix
processor. The following table describes the structure of the input image.
Offset Description Length
0 Write Block ID 1
1 to 40 Read Data 40
41 Read Block ID 1
The Read Block ID is an index value used to determine the location of where the
data will be placed in the ControlLogix processor controller tag array of module
read data. Each transfer can move up to 40 words (block offsets 1 to 40) of data.
In addition to moving user data, the block also contains status data for the
module.
The Write Block ID associated with the block requests data from the ControlLogix
processor. Under normal program operation, the module sequentially sends read
blocks and requests write blocks.
For example, if the application uses three read and two write blocks, the
sequence will be as follows:
R1W1→R2W2→R3W1→R1W2→R2W1→R3W2→R1W1→
This sequence will continue until interrupted by other write block numbers sent by
the controller or by a command request from a node on the Modbus network or
operator control through the module’s Configuration/Debug port.
Block Request from Processor to Module
These blocks of data transfer information from the ControlLogix processor to the
module. The following table describes the structure of the output image.
Offset Description Length
0 Write Block ID 1
1 to 40 Write Data 40
41 Spare 1
The Write Block ID is an index value used to determine the location in the
module’s database where the data will be placed. Each transfer can move up to
40 words (block offsets 1 to 40) of data.