Yaskawa F7 Modbus - Manual (Page 19)

Message Formats 2-2
Read Multiple Registers – Function Code 03H
The Read Multiple Register message is used to read the contents of from one to eight consecutive registers. The formats of the read command
and response messages are shown below.
► Read Multiple Registers Command Message
Table 2.2 - Read Command Message
Description Data
Slave Address 02h
Function Code 03h
Upper 00h
Starting Register
Lower 20h
Upper 00h
Quantity
Lower 04h
Upper 45h
CRC-16
Lower F0h
Each F7 drive slave address is set via. parameter H5-01. Valid slave addresses must be in the range of 1 to 20 hex (1 to 32 dec) and entered as a
hexadecimal number. No two slaves may have the same address. The master addresses the slave by placing the slave address in the Slave
Address field of the message. In the command message above, the slave is addressed at 02h. Broadcast address 0 is not valid for register read
commands.
The function code of this message is 03h (read multiple registers).
The starting register is the address of the first register to be read. In the command message above the starting register address is 20h (0020h).
The quantity indicates how many consecutive registers are to be read. The quantity may range from 1 to 8 registers. If an invalid quantity is
entered, error code 03h is returned in a fault response message. In this example, four consecutive registers are to be read: 20h, 21h, 22h and 23h.
A CRC-16 value is generated from a calculation including the message slave address, function code, starting register and quantity. The
procedure for calculating a CRC-16 is described at the end of this chapter. When the slave receives the command message it calculates a CRC-
16 value and compares it to the CRC-16 of the command message. If the two CRC-16 values are identical and the Slave Address is correct, the
slave processes command message. If the two CRC-16 values are not identical, the slave will discard the command message and not respond.
If the command message has a valid slave address, function code, starting register, and quantity, the slave will respond with a normal response
message. If the command message has an invalid function code, starting register, and/or quantity, the slave will respond with a fault response
message. If the command message has an invalid slave address or CRC-16, no response will be returned.