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8. Communication Protocol
8.1 Overview
PMAC735 main unit provides the MODBUS-RTU communication protocol, 8 data bits, 1 stop bit,
without check bit. Each frame data package contains the address field, functional code field, data
field, and check field. The maximum length of each data package is 95 bytes.
The length of the address field is 1 byte, and the content is slave station address. The range of an
effective slave station address is 1 to 247. If the slave station receives a package in which the
address field information conforms to its own address, it should execute the commands contained
in the package. In the package to which the slave station responds, the field is its own address.
The length of the functional code field is 1 byte, used to tell the slave station to execute what
operations. The functional codes supported by PMAC735 are listed in the table below:
Functional code
Meaning
Function
0x03
Read register
Obtaining one or more than one current register
values inside the current PMAC735.
0x10
Setting register
Writing the designated values into one or more than
one registers inside PMAC735.
0x05
Relay control
Controlling a relay inside the current PMAC735.
The length of the data field is not fixed, and it will be defined according to the specific function.
The data in the data field adopts the BIG INDIAN mode, with the high bytes in front and the low
bytes at the back.
The check field adopts 16-bit CRC check codes. The transmitting device should make CRC
calculation for each of the data inside the package, and the final results will be stored in the check
