E 113) – ProSoft Technology MVI56E-MNET/MNETXT User Manual
Page 113
MVI56E-MNET / MNETXT ♦ ControlLogix Platform
Reference
Modbus TCP/IP Interface Module
User Manual
ProSoft Technology, Inc.
Page 113 of 181
April 23, 2014
5.2.1 Normal Data Transfer Blocks
Normal data transfer includes the paging of user data from the m
odule’s internal
database (registers 0 to 4999), as well as paging of status data. These data are
transferred through read (input image) and write (output image) blocks.
The following topics describe the function and structure of each block.
Read Block
These blocks of data transfer information from the module to the ControlLogix
processor.
The following table describes the structure of the input image.
Read Block from Module to Processor
Word Offset
Description
Length
0
Reserved
1
1
Write Block ID
1
2 to 201
Read Data
200
202
Program Scan Counter
1
203 to 208
Block Transfer Status
6
209
Product Code 1
1
210
Product Code 2
1
211
Version number
1
212 to 218
Not Used
7
219 to 221
Reserved
2
222 to 228
MNet Server Status
7
229 to 231
Reserved
2
232 to 238
MBAP Server Status
7
239 to 248
MNet Client Status
10
249
Read Block ID
1
The Read Block ID is an index value used to determine where the 200 words of
data from module memory will be placed in the ReadData[x] controller tag array
of the ControlLogix processor. Each transfer can move up to 200 words (block
offsets 2 to 201) 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.
During 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.