Serial Communication Programmer Reference Guide
Powermax65/85/105 SYNC Reference Guide 810400 9
Modbus request and response message frame format
Each segment is explained as follows.
Start Node Address Function Data LRC End
1 character
:
2 characters 2 characters 0 up to 2x252 characters 2 characters 2 characters
<CR><LF>
Segment Description
Start All messages must start with a colon (:). This character identifies that a new message
follows.
Node Address In a request message: These characters identify the unique address (node address) of
the plasma power supply to which the request message is being sent.
In a response message: These characters identify its node address to confirm that the
correct plasma power supply responded.
Function In a request message: The function code tells the plasma power supply what to do. If
needed, the Data characters provide additional information about how to do the function.
In a response message: The function code confirms the function that was done by the
plasma power supply.
In an error response message: The Function segment of the message is different. Refer
to page 10.
Data In a request message: These characters can be included to provide additional
information about how to do the function. This can include items like discrete and register
addresses, the quantity of items to be handled, and the count of actual data bytes in the
field.
In a response message: These characters represent the result of the function done by
the plasma power supply.
In an error response message: The Data segment of the message is different. Refer to
page 10.
LRC These characters are used to perform a Longitudinal Redundancy Check (LRC), a method
for performing a checksum on the message.
In a request message: The LRC value is calculated by the CNC. When the plasma
power supply receives the request message, it also calculates an LRC for the request
message. If the LRCs are the same, the plasma power supply accepts the request
message.
For more information on how to calculate an LRC, refer to page 12.
In a response message: The LRC value is calculated by the plasma power supply for the
data in its response message. The CNC performs a checksum before accepting the
response message.
<CR><LF> These characters identify the end of the message.
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