6.2 Modbus Communications
220 SIEPYEUOQ2A01A AC Drive Q2A Technical Manual
Figure 6.8 CRC-16 Calculation Example
Response Data
The drive does the CRC-16 calculation for the response message and makes sure that the data does not have
errors. Make sure that the calculated value is the same value as the CRC-16 in the response message.
◆ Examples of Messages for Commands/Responses
The items in this section are examples of messages for commands/responses.
■ Read the Description of Holding Register
Uses function code 03 (Hex.) to read the contents of a maximum of 16 holding registers.
The following figure shows example messages when the drive reads status signal from the drive of slave 2, the
error contents, fault contents, and frequency references.
Figure 6.9 Message Example When Reading the Contents of Holding Register
Description Calculation Overflow Description Calculation Overflow
Initial value (FFFF(Hex.))
1111 1111 1111 1111
0000 0010
1111 1111 1111 1101
0111 1111 1111 1110
1
1
0
1
0
1
0
1
1
1
0
1
0
1
1
1
1010 0000 0000 0001
1101 1111 1111 1111
0110 1111 1111 1111
1010 0000 0000 0001
1100 1111 1111 1110
0110 0111 1111 1111
0011 0011 1111 1111
1010 0000 0000 0001
1001 0011 1111 1110
0100 1001 1111 1111
0010 0100 1111 1111
1010 0000 0000 0001
1000 0100 1111 1110
0100 0010 0111 1111
0010 0001 0011 1111
1010 0000 0000 0001
1000 0001 0011 1110
0000 0011
1000 0001 0011 1101
0100 0000 1001 1110
1010 0000 0000 0001
1110 0000 1001 1111
0111 0000 0100 1111
1010 0000 0000 0001
1101 0000 0100 1110
0110 1000 0010 0111
0011 0100 0001 0011
1010 0000 0000 0001
1001 0100 0001 0010
0100 1010 0000 1001
0010 0101 0000 0100
1010 0000 0000 0001
1000 0101 0000 0101
0100 0010 1000 0010
1010 0000 0000 0001
1110 0010 1000 0011
0111 0001 0100 0001
1010 0000 0000 0001
1101 0001 0100 0000
1101 0001 0100 0000
041D
Address 02 (Hex.)
XOR w initial value
Shift 1
Shift 2
Shift 3
Shift 4
Shift 5
Shift 6
XOR w A001 (Hex.)
XOR w A001 (Hex.)
XOR w A001 (Hex.)
Shift 7
Shift 8
XOR w A001 (Hex.)
XOR w A001 (Hex.)
XOR result
XOR result
XOR result
XOR result
XOR result
Shift 1
Shift 2
Shift 3
Shift 4
Shift 5
Shift 6
XOR w A001 (Hex.)
XOR w A001 (Hex.)
XOR w A001 (Hex.)
Shift 7
XOR w A001 (Hex.)
XOR result
XOR w result
Function code 03 (Hex.)
XOR result
XOR result
XOR result
Shift 8
XOR w A001 (Hex.)
XOR result
XOR w A001 (Hex.)
XOR result
CRC-16
(Lower) (Upper)
Continue from here with next data.
Perform operations with next data (function code)
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