Yaskawa F7 Modbus - Manual (Page 23)

Message Formats 2-6
Loop-Back Test – Function Code 08H
The Loop-Back Test is used to verify that the communications parameters for the F7 drive have been set correctly and that the connection is
correct. The message should be constructed exactly as shown below. If everything is set and connected correctly, the received response will
match the response shown below.
► Loop-Back Test - 08h
The Loop-Back test function (08h) is used for checking signal transmission between master and slaves. The command message format is shown
below.
Table 2.8 - Loop-Back Command Message
Description Data
Slave Address 01h
Function Code 08h
Upper 00h
Test Code
Lower 00h
Upper A5h
Data
Lower 37h
Upper DAh
CRC-16
Lower 8Dh
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 01h. Broadcast address 0 is not valid for Loop-Back test
commands.
The function code of this message is 08h (Loop-Back test).
The test code must be set to 0000h. This function specifies that the data passed in the command message is to be returned (looped back) in the
response message.
The Data section contains arbitrary values.
A CRC-16 value is generated from a calculation including the message slave address, function code, test code, and data. 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, test code, data and CRC-16, the slave will respond with the normal response
message. If the command message has an invalid function code, test code, and/or data, 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.