ProSoft Technology MVI69E-MBTCP - Manual (Page 70)

MVI69E-MBTCP Backplane Data Exchange MVI69E-MBTCP ♦ CompactLogix Platform
User Manual Modbus TCP/IP Enhanced Communication Module
Page 70 of 150 ProSoft Technology, Inc.
May 20, 2015
4.4 Data Flow Between the Module and Processor
The following topics describe the flow of data between the two pieces of
hardware (CompactLogix processor and MVI69E-MBTCP module) and other
nodes on the Modbus network. The module can act as a Modbus TCP/IP client
(master), server (slave), or both simultaneously.
4.4.1 Server Mode
In Server driver mode, the MVI69E-MBTCP module responds to read and write
commands issued by a client on the Modbus network. The following diagram
shows the data flow for normal Server mode.
Step Description
1 Any time the module restarts (boots or reboots), the server port driver receives
configuration information from the MBTCP controller tags. This information configures the
Ethernet port and defines Server driver characteristics. The configuration information may
also contain instructions to offset data stored in the database to addresses different from
addresses requested in the received messages.
2 A Modbus client device, such as a Modicon PLC or an HMI application, issues a read or
write command to the module’s IP address. The Server driver qualifies the message before
accepting it into the module. Rejected commands cause an Exception Response.
3 After the module accepts the command, the data is immediately transferred to or from the
module’s internal database. On a read command, the data is read from of the database and
a response message is built. On a write command, the data is written directly into the
database and a response message is built.
4 After Steps 2 and 3 have been completed, either a normal response message or an
Exception Response message is sent to the client.
5 Counters are available in the Status Block to permit the ladder logic program to determine
the level of activity of the Server driver.