DL205 User Manual, 4th Edition, Rev. D
4-41
Chapter 4: System Design and Configuration
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Network Master Operation
This section describes how the DL250–1 and DL260 can communicate on a Modbus or
DirectNET network as a master. For Modbus networks, it uses the Modbus RTU protocol,
which must be interpreted by all the slaves on the network. Both Modbus and DirectNET are
single master/multiple slave networks. The master is the only member of the network that can
initiate requests on the network. This section teaches you how to design the required ladder
logic for network master operation.
When using the DL250–1 or DL260 CPU
as the master station, you use simple RLL
instructions to initiate the requests. The
WX instruction initiates network write
operations, and the RX instruction initiates
network read operations. Before executing
either the WX or RX commands, we will
need to load data related to the read or write
operation onto the CPU’s accumulator
stack. When the WX or RX instruction
executes, it uses the information on the stack
combined with data in the instruction box
to completely define the task, which goes to
the port.
The following step-by-step procedure will provide the information necessary to set up your
ladder program to receive data from a network slave.
Slave #1 Slave #3
Master
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