ProSoft Technology MVI56-MCM, Руководство пользователя

Страница: 49 / 159

Configuration as a Modbus Slave MVI56-MCM ♦ ControlLogix Platform
Modbus Communication Module
ProSoft Technology, Inc. Page 49 of 159
July 24, 2008
5 Configuration as a Modbus Slave
In This Chapter
™ Overview ............................................................................................... 49
™ ModDef Settings.................................................................................... 50
™ Read and Write Same Modbus Address (Pass Thru)............................ 54
™ Slave Configuration ............................................................................... 56
™ Further clarification for some parameters in table above....................... 57
™ Float Point Data Handling...................................................................... 57
5.1 Overview
When configuring the module as a slave, you will be providing whoever is
programming the master side of the communications with a Modbus Memory
Map.
Note: Utilizing the Sample Ladder Logic, the transfer of data is already done.
Information that is to be read by the Modbus Master device will be placed in the
MCM.DATA.WriteData array as this will be pushed out to the module so that
values from the ControlLogix processor can be read by the Modbus Master.
Information that must be written to the ControlLogix processor from the Modbus
Master device will be placed into the MCM.DATA.ReadData array.
To set up module as a Modbus Slave you must determine how much data you
must transfer to and from the module, to the Modbus Master.
The sample ladder file is setup to transfer 600 16 bit registers in each direction. If
more than that is required, please see Applications Requiring More Than 600
Registers of ReadData or WriteData (page 27).
Find out if the master can read from one Modbus address and write to another
Modbus address, or, if the master must use the same address to read and write
data points.
If the master must read and write to the exact same Modbus address, then a
mode of operation called Pass Thru must be used.
This allows the MCM.DATA.WriteData array to be used for all data transfer to the
master. Because the data transfer of the MVI56-MCM module cannot be
bidirectional, in Pass Thru mode when a Modbus Write command is issued by
the Master, the MVI module builds a special block of information. This block is
then parsed by the ladder logic, and the value written from the Modbus Master is
then updated in the MCM.DATA.WriteData array.