FIGURE 32 - PLC ASSEMBLY CONCEPT
So, no matter which of the three connection protocols you use (Modbus TCP, EIP, or Profinet I/O), for any given
assembly, the internal data you are accessing with your PLC is the same.
MODBUS ASSEMBLY INSTANCE STRUCTURE
Each ConveyLinx-IO utilizes Modbus register architecture for remote data access over Ethernet. Modbus TCP is a
simple protocol for data exchange based upon a query/response mechanism. Each module’s memory structure
contains a fixed array of internal data locations that are constructed as Modbus Holding Registers. Each module
has a fixed reserve of Holding Registers with each capable of holding a 16-bit numerical integer value. Modbus TCP
protocol provides for read/write access to any available Holding Register. The structure of these registers allows
for individual module’s to read from and write to specific register address locations to achieve inter-module
communications. Certain registers are read from and written to by the EasyRoll software in order to monitor
and/or change default configuration values.
Modbus TCP addressing convention utilizes a “4:xxxx” notation. The “4:” in Modbus
protocol designates that the address is a Holding Register and the xxxx is a numerical
value representing the offset or index for a specific location. The “xxxx” values used in
this document are to be interpreted as if they are for a Modbus PLC which means that the
first register address is “4:0001” and that there is no “4:0000” register. Some PLC data
structures and PC development environments utilize the “4:0000” designation and their
indexes will be offset by 1. Please refer to your PLC or PC application documentation for
the Modbus convention used on their platforms.
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