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Configuration as a Modbus Master
MVI56-MCM
♦
ControlLogix Platform
Modbus Communication Module
ProSoft Technology, Inc.
Page 31 of 159
July 24, 2008
4.2.2 Master Command Configuration
The following section describes the communications with the master port and the
slave devices that are connected to that port.
Verify you are in Monitor Tags mode. Then use the scroll bar at bottom to view
description of each parameter. The following table uses that information.
Label Description
Enable
0 = Disabled
Command will not be executed, but can be enabled using command
control option in ladder logic.
1 = Enabled
Command is enabled and will be sent out to the target device.
2 = Conditional Write
Only for Func 5, 15, 6, or 16 data will be written out to the target device
only when the data to be written has changed.
IntAddress
Determines where in the module's 5000 register database the data will
be stored to or written from. On a Read command this will determine
once the information has been read from a slave, where it will be placed
in the module database. On read commands you will want to configure
this for a location that is setup for ReadData. The internal database
location of the ReadData and WriteData tags is determined by the
configuration setup in the MCM.ModDef tag location.
For write data the IntAddress will determine where to obtain the
information to be written out to the slave device. This will need to be a
location that is setup as WriteData.
Note:
When using a bit level command you will want to define this field
at the bit level. For instance, when using a function code 1, 2 for a Read
command you will need to have a value of 16000 to place the data in
MCM.ReadData[0] (register 1000 * 16 bits per register = 16000).
PollInt
Values in this field will represent the number of seconds that a master
device will wait before issuing this command.
Count
Sets how many continuous words (FC 3, 4, and 16) or bits (FC 1, 2 and
15) will be requested from the slave device.
Valid values are 1 to 125 words for function codes 3, 4 and 16, while
you can specify a range of 1 to 2000 for function codes 1, 2 and 15.
Note: These values are maximum allowed within Modbus protocol,
some devices may support less than maximum allowed.