ProSoft Technology MVI71-MNET - Manual (Page 61)

Reference MVI71-MNET ♦ PLC Platform
User Manual Modbus TCP/IP Interface Module
ProSoft Technology, Inc.
Page 61 of 109
June 23, 2009
The following illustration shows the data transfer method used to move data
between the PLC processor, the MVI71-MNET module and the Modbus TCP/IP
Network.
All data transferred between the module and the processor over the backplane is
through the BTR and BTW blocks. Ladder logic must be written in the PLC
processor to interface the block data with user data files. All data used by the
module is stored in its internal database. The following illustration shows the
layout of the database:
Module’s Internal Database Structure
5000 registers for user data 0
Register Data
4999
Data contained in this database is paged through the block transfer interface by
coordination of the PLC ladder logic and the MVI71-MNET module's program. Up
to 64 words of data can be transferred from the module to the processor at a
time. Up to 64 words of data can be transferred from the processor to the
module. The read and write block identification codes in each data block
determine the function to be performed or the content of the data block.