Omron Q2A Series Technical Manual page 219

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Slave Address
Set the slave address of the drive to 00 to FF (Hex.). When the slave address is 00 (Hex), the master sends the
command and all slaves receive the command.
The slave will not send a response message to the master.
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Function Code
There are five function codes that set commands.
Function Code Subfunction Code
(Hex.) (Hex.)
03 -
08 -
10 -
5A -
010D
67
010E
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Communications Data
Communications data is a series of data that uses the combination of the communications register number and the
data for these registers. The data length changes when the description of the command changes. For a loopback
test, it switches to test code.
The communications register for the drive has a 2-byte length. Data that is written to the register for the drive is
usually 2 bytes. Register data that is read from the drive is also 2 bytes.
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Error Check
Error check uses the CRC-16 method to detect transmission errors. Use the procedure in this section to calculate
CRC-16.
Command Data
When the drive receives data, it will make sure that there are no errors in the data. The drive uses the procedure
below to calculate CRC-16, then compares that data with the CRC-16 value in the message. If the CRC-16 values
do not agree, the drive will not execute a command message.
When you calculate CRC-16 in Modbus communications, make sure that you set the start value as FFFF (Hex.).
All 16 bits must be 1.
Use this procedure to calculate CRC-16:
1. Make sure that the start value is FFFF (Hex.).
2. Calculate the FFFF (Hex.) start value and the XOR of the slave address (exclusive OR).
3. Move the step 2 results one column to the right. Do this shift until the carry bit is 1.
4. When the carry bit is 1, calculate XOR via the result from the above step 3 and A001 (Hex.).
5. Do steps 3 and 4 until the 8th shift to the right.
6. Use the result of step 5 to calculate the XOR and the data of the following messages (function code, register
address, data). Do steps 3 to 5 until the last data, then calculate.
7. The result of the last right shift or the value of the last XOR calculation is the result for CRC-16.
The following figure lists examples of the CRC-16 calculation of slave address 02 (Hex.) and function code 03
(Hex.). The calculated results of CRC-16 for this section is D140 (Hex.).
Note:
The calculation example only gives information about some error checks with CRC-16. The drive will do the same error checks for the
next data.
SIEPYEUOQ2A01A AC Drive Q2A Technical Manual
Table 6.5 Function Codes
Command Message
Minimum Data
Function
Length
(byte)
Read the Description of
8
Holding Register
Loopback Test 8
Writing to Multiple
11
Holding Registers
Writing to Multiple
Holding Registers /
11
Reading the Register
Indicated
Reading Contents of
Non-Consecutive 10
Holding Registers
Writing to Non-
Consecutive Holding 14
Registers
6.2 Modbus Communications
Response Message
Maximum Data Minimum Data
Length Length
(byte) (byte)
8 7
8 8
41 8
41 17
248 10
250 8
Maximum Data
Length
(byte)
37
8
8
17
248
8
6
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