Normal Data Transfer Blocks - ProSoft MVI56E-MNETCR User Manual

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5.2.1 Normal Data Transfer Blocks

Normal data transfer includes the paging of user data between the processor's
data areas and the module's internal database (registers 0 to 4999), as well as
the paging of status data. These data are transferred through Read (input
image), Write (output image) and Status blocks. The data is paged 40 words at a
time.
During normal program operation, the module sequentially sends Read and
Status Data blocks and receives Write blocks. The Status block is first in the
sequence, followed by alternating Write and Read blocks.
As an example, assume that an application's Read Data area consists of 120
words and its Write Data area consists of 80 words. Since the Read and Write
data is paged 40 words at a time, the module will use 3 Read blocks and 2 Write
blocks to transfer the data. The Read, Write and Status blocks will be sequenced
as follows.
This sequence will continue until interrupted by other special function blocks sent
by the processor, by a command request from a node on the Modbus network, or
by operator control through the module's Configuration/Debug port.
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
0
1 to 40
41
The Read Block ID is an index value used to determine where the 40 words of
data from module memory will be placed in the ReadData[x] controller tag array
of the ControlLogix. Each transfer can move up to 40 words (block offsets 1 to
40) of data.
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Modbus TCP/IP Multi-Client Enhanced Communications Module for Remote Chassis
Description
Write Block ID
Read Data
Read Block ID
MVI56E-MNETCR ♦ ControlLogix Platform
Length
1
40
1
ProSoft Technology, Inc.