ProSoft Technology MVI46-MCM - Manual (Page 73)

MVI46-MCM ♦ SLC Platform Reference
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 73 of 108
March 29, 2011
5.2.5 Data Flow Between MVI46-MCM Module and SLC Processor
The following topics describe the flow of data between the two pieces of
hardware (SLC processor and MVI46-MCM module) and other nodes on the
MODBUS network under the module’s different operating modes. Each port on
the module is configured to emulate a MODBUS master device or a MODBUS
slave device. The operation of each port depends on this configuration.
Slave Driver
The Slave Driver Mode allows the MVI46-MCM module to respond to data read
and write commands issued by a master on the MODBUS network. The following
flow chart and associated table describe the flow of data in and out of the
module.
Step Description
1 The MODBUS slave port driver receives the configuration information from the SLC
processor. This information configures the serial port and defines the slave node
characteristics.
2 A Host device, such as the Rockwell Automation PLC or an HMI application issues a
read or write command to the module’s node address. The port 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 the M1 file and a response
message is built.
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 Slave Driver.