ProSoft Technology MVI71-MCM - Manual (Page 58)

MVI71-MCM ♦ PLC Platform Reference
Modbus Communication Module
Page 58 of 111 ProSoft Technology, Inc.
December 28, 2007
Side-Connect
Modbus
Port
Drivers
Master
Driver
Logic
Master
Driver
Logic
Slave
Driver
Logic
Slave
Driver
Logic
Module’s
Internal
Database
MVI71 - MCM Module
To Modbus
Network
User Data Files
PLC5 Processor
Status
Read Data
Write Data
Special Control
Blocks
When the side connect interface is used, data is transferred directly between the
processor and the module. The module's program interfaces directly to the set of
user data files established in the PLC to pass all data between the two devices.
No ladder logic is required for data transfer, only the establishment of the data
files.
All data transferred between the module and the processor over the backplane is
through the input and output images. Ladder logic must be written in the PLC
processor to interface the input and output image data with data defined in the
data registers. All data used by the module is stored in its internal database. This
database is defined as a virtual Modbus data table with addresses from 0 (40001
Modbus) to 6999 (47000 Modbus). The following illustration shows the layout of
the database:
5000 registers for user data
Register
Data
Status
and
Config
Module’s Internal Database
0
4999
5000
7999
3000 words of configuration
and status data
Data contained in this database is paged through the input and output images by
coordination of the PLC ladder logic and the MVI71-MCM module's program. Up
to 60 words of data can be transferred from the module to the processor at a
time. Up to 60 words of data can be transferred from the processor to the
module. Each image has a defined structure depending on the data content and
the function of the data transfer as defined below.