MVI56-MCM
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ControlLogix Platform
Configuration as a Modbus Master
Modbus Communication Module
Page 32 of 159
ProSoft Technology, Inc.
July 24, 2008
Label Description
Swap
Typically used when reading floating point data, swaps the data read
from the slave device before it is placed into the module memory. For
instance, you receive 4 bytes of data from the slave (ABCD).
0 = No swapping (ABCD)
1 = Word pairs switched (CDAB)
2 = Bytes and words switched (DCBA)
3 = Bytes swapped (BADC)
Node
Node address of the device on the network to read data from, or write
data to. Valid addresses are 1 to 247 with address 0 being reserved for
broadcast write commands (will broadcast a Write command to all
devices on the network).
Func
Determines the modbus function code that will be issued in the
command to the slave device. Valid values for this field are as follows:
1 = Read Coil Status
This will read modbus addresses 0001 to 9999. These are bit values
used to indicate coil status, and can also be written to using Function
Code 5 or 15.
2 = Read Input Coils
This will read modbus addresses 10001 to 29999. Like Function Code
1, these are also bit values, but Function Code 2 values are Read Only
data values, while FC 5 and 15 will write to the Coil Status values.
3 = Read Holding Registers
This is to be used for Modbus addresses 40001 to 47999. This is a 16
bit word value, and can be written to using Function Codes of 6 and 16.
4 = Read Input Registers
Will read modbus addresses 30001 to 39999. These are also 16 bit
word values, but are Read Only data, and cannot be written to by the
master.
5 = Write Single Coil Status
This will write to modbus addresses 0001 to 9999. This command will
write to only one coil. If you want to write to multiple coils you will need
to use Function Code 15.
6 = Write Single Register
For modbus addresses 40001 to 47999. This will write one single
register value out to a slave device. For multiple register writes you will
need to use Function Code 16.
15 = Multiple Coil Write
This function code will write multiple coil values to the slave addresses
0001 to 9999.
16 = Multiple Register Write
Will write multiple register values to the slave device at addresses
40001 to 49999.
