ProSoft Technology MVI71-MNET - Manual (Page 75)

Reference MVI71-MNET ♦ PLC Platform
User Manual Modbus TCP/IP Interface Module
ProSoft Technology, Inc.
Page 75 of 109
June 23, 2009
5.2.2 Data Flow between MVI71-MNET Module and PLC Processor
The following topics describe the flow of data between the two pieces of
hardware (PLC processor and MVI71-MNET module) and other nodes on the
Modbus TCP/IP network under the module’s different operating modes. The
module contains both servers and a client. The servers accept TCP/IP
connections on service ports 502 (MBAP) and 2000 (MNET). The client can
generate either MBAP or MNET requests dependent on the service port selected
in the command.
Server Driver
The Server Driver allows the MVI71-MNET module to respond to data read and
write commands issued by clients on the Modbus TCP/IP network. The following
flow chart and associated table describe the flow of data into and out of the
module.
1 The server driver receives the configuration information from the
configuration file on the Compact Flash Disk, and the module initializes the
servers.
2 A Host device, such as a Modicon PLC or an HMI application issues a read
or write command to the module’s node address. The server driver qualifies
the message before accepting it into the module.
3 After the module accepts the command, the data is immediately transferred
to or from the internal database in the module. If the command is a read
command, the data is read out of the database and a response message is
built. If the command is a write command, the data is written directly into the
database and a response message is built. If the pass-through feature is
utilized, the write message is transferred directly to the processor and is not
written to the module’s database.
4 After the data processing has been completed in Step 3, the response is
issued to the originating master node.
5 Counters are available in the Status Block that permit the ladder logic
program to determine the level of activity of the Server Driver.