Rockwell Automation 20-COMM-M Modbus/TCP Adapter - Manual (Page 37)

20-COMM-M Modbus/TCP Adapter User Manual
Publication 20COMM-UM014C-EN-P
Chapter 4
Using Modbus/TCP Function Codes
This chapter provides information about controlling a PowerFlex 7-Class
drive, setting its Reference, and accessing its parameters and the parameters
of its connected peripherals using Modbus/TCP Function Codes over the
Modbus/TCP network.
Understanding Modbus/TCP The Modbus/TCP protocol is a messaging structure used to establish
master-slave communication between intelligent devices. The protocol
defines the format of the messages.
Messages from a master to a slave contain the address of the slave, a
Function Code defining the requested action, and any data to be sent.
Messages from a slave to a master contain fields confirming the action taken
and any data to be returned. If an error occurred in the receipt of the
message or if the slave is unable to perform the requested action, the slave
will construct an error message and send it as its response.
Modbus/TCP can access a single address or multiple addresses
simultaneously, either reading or writing single-bit values, 16-bit values, or
32-bit values.
Important: Modbus/TCP devices can be 0-based (register addresses
numbered starting at 0) or 1-based (register addresses
numbered starting at 1). The convention in this manual is
1-based. Depending on the Modbus/TCP master used, the
register addresses listed in this chapter may need to be offset by
“-1.” For example, Logic Command is register address 10001
for some master devices and register address 10000 for others.
Topic Page
Understanding Modbus/TCP 4-1
Using the I/O 4-3
Accessing Device Parameters 4-9
Using Datalinks 4-12
Supported Modbus Registers 4-15
TIP: When using a Modbus/TCP controller that provides a selection for
Internet Protocol (IP), select Ethernet II framing since it is used by the
adapter. Do not select IEEE 802.3 LLC/SNAP framing.