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9 Communications Functions
High-function General-purpose Inverter RX2 Series User’s Manual
9-2 Modbus Method
9
CRC-16 Polynomial Calculation Example
<Header/Trailer (Silent Interval)>
• The silent interval is the length of time during which the inverter waits after receiving a query from the
master, before sending back a response to it.
• Be sure to include a silent interval of 3.5 characters (3.5 bytes) as the wait time. If less than 3.5 char-
acters, the inverter will send no response.
• The actual wait time during communications is the sum of the silent interval (3.5 characters) and the
Communication Wait Time (CF-07).
<Required Communications Time>
• The time that the inverter takes to send a response after receiving a query is the sum of the silent
interval (3.5 characters) and the Communication Wait Time (CF-07).
• After receiving a response from an inverter, be sure to include an interval equivalent to the silent
interval (3.5 characters) or more before sending the next query to the inverter.
<Normal Response>
• If a query includes the loop-back function code (08 hex), the inverter sends back a response with the
same content as that of the query.
• If a query includes a function code for writing data to a holding register/coil (05 hex, 06 hex, 0F hex,
10 hex), the inverter returns the query as a response.
• If a query includes a function code for reading data from a holding register/coil (01 hex, 03 hex), the
inverter sends back a response that includes the same slave address and function code as the query,
with the read data.
Response Frame Configuration
CRC-16
calculation
CRC = FFFFh
CRC
Hi Lo
CRC register (2 bytes)
Target data
Exists
All target data
completed
Interchange the Hi and
Lo bytes of CRC
Completed
CRC = CRC XOR target data
8-bit shift
Completed
Bits left
Shift CRC = CRC by 1 bit to the right
0
1
Overflow bit
after shift
CRC = CRC XOR A001h
Shift by 1 byte against target data
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