C.7 Message Format
YASKAWA ELECTRIC SIEP C710616 27G YASKAWA AC Drive A1000 Technical Manual 555
MEMOBUS/Modbus
Communications
C
C.7 Message Format
Message Content
In MEMOBUS/Modbus communications, the master sends commands to the slave, and the slave responds. The message
format is configured for both sending and receiving as shown below, and the length of data packets depends on the
command (function) content.
Slave Address
The slave address in the message defines the note the message is sent to. Use addresses between 0 and FF (hex). If a
message with slave address 0 is sent (broadcast), the command from the master will be received by all slaves. The slaves
do not provide a response to a broadcast type message.
Function Code
The three types of function codes are shown in the table below.
Data
Configure consecutive data by combining the MEMOBUS/Modbus register address (test code in case of a loopback test)
and the data the register contains. The data length changes depending on the command details.
A drive MEMOBUS/Modbus register always has a data length of t
wo bytes. Therefore data written into drive registers
must also always have a length of two bytes. Register data read out from the drive will always consist of two bytes.
Error Check
The drive uses a CRC-16 (cyclic redundancy check, checksum method) for checking data validity. Use the procedure
described below when calculating the CRC-16 checksum for command data or when verifying response data.
Command Data
When the drive receives data, it calculates the CRC-16 checksum from the data and compares it to the CRC-16 value
received within the message. Both must match before a command is processed.
An initial value of FFFFH (i.e., all 16 bits equal
1) must be used for CRC-16 calculations in the MEMOBUS/Modbus
protocol.
Calculate the CRC-16 checksum using the
following steps:
1. The starting value is FFFFH.
2. Perform an XOR operation of this value and the slave address.
3. Right shift the result.
4. When the overflow bit of the shift operation becomes 1, perform an XOR operation of the result from step 3
above and the fix value A001H.
5. Repeat steps 3 and 4 until eight shift operations have been performed.
Function
Code
Function Name
Data Length (bytes)
Command Message Response Message
Minimum Maximum Minimum Maximum
03H Read MEMOBUS/Modbus registers 8 8 7 37
08H Loopback test 8888
10H Write to multiple MEMOBUS/Modbus registers 11 41 8 8
SLAVE ADDRESS
FUNCTION CODE
DATA
ERROR CHECK
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