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Fig. 4.
Router Program
4 MPCS Protocol
MPCS is important to have a protocol at the application layer that allows PLCs to take
advantage of producer/consumer services. Using producer/consumer, the data "pro-
ducer" which is a PLC, puts the PAN Coordinator ID at the front of each packet. The
message is then sent out of the network and the Coordinator screens the ID to deter-
mine if the data is for its consumption. If so, the Coordinator becomes the "con-
sumer." As a result, multi-cast communication happens naturally and efficiently in a
producer/consumer service.
MODBUS is designed for source/destination communication or master/slave
model. MPCS, however, joins forces with producer/consumer technology to offer a
superior message-delivery mechanism of MODBUS. MPCS supports all of the major
communication relationships of MODBUS. MPCS is a flexible protocol and results in
efficient use of bandwidth.
MODBUS-compliant devices are common in industrial application. Users can
achieve MODBUS by device's internal standard, direct interface and external con-
verter. Internal standard means MODBUS is the basic protocol that PLC uses for
parsing messages, such as Modicon and XINJIE controllers. Some PLCs have their
internal standard protocols, but these PLCs also provide MODBUS communication
interface and MODBUS communication instruction. For example, The MicroLogix
controller family of Rockwell Automation supports RS-485, direct interface to
MODBUS RTU master-slave networks without an external electrical interface con-
verter. These PLCs are internal support MODBUS. In order to use MODBUS proto-
col, some PLCs must add some external electrical interface converter, such as Sie-
mens S7-300 and S7-400.
In this experiment system, MODBUS is internal standard of XINJIE controller.
Microwin 4.0, which is the program software of S7-224, provides MODBUS
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