YASKAWA GA700 - Page 296

5.3 MEMOBUS/Modbus Communications
296 YASKAWA ELECTRIC SIEP C710617 05F YASKAWA AC Drive GA700 Technical Manual
■ 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.
■ Function Code
There are five function codes that set commands. Table 5.5 shows the different codes.
Table 5.5 Function Codes
Function Code
(Hex.)
Subfunction
Code
(Hex.)
Function
Command Message Response Message
Minimum Data
Length
(byte)
Maximum Data
Length
(byte)
Minimum Data
Length
(byte)
Maximum Data
Length
(byte)
03 -
Read the
Description of
Holding Register
8 8 7 37
08 - Loopback Test 8 8 8 8
10 -
Writing to
Multiple Holding
Registers
11 41 8 8
5A -
Writing to
Multiple Holding
Registers /
Reading the
Register Indicated
11 41 17 17
67
010D
Reading Contents
of Non-
Consecutive
Holding Registers
10 248 10 248
010E
Writing to Non-
Consecutive
Holding Registers
14 250 8 8
■ 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.
■ 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 MEMOBUS/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.