Loop-Back Test - 08H - YASKAWA GPD 515/G5 Modbus RTU Technical Manual

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.
Each GPD 515ís slave address is set in advance by the drive parameter H5-01. Valid slave
addresses must be in the range of 1 to 31 decimal (1 to 1F hex). No two slaves may have the
same address. The master addresses the slave by placing the slave address in the address field
of the message. In the command message above, the slave is addressed at 1.
The function code of this message is 08h (loop-back test).
The test code must be set to ë0000í. 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 data values. These data values are used to verify that the
slave receives the correct data.
A CRC-16 value is generated from a calculation using the values of the address, function code,
test code, and data sections of the message. 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 one in CRC-16 field of the command message.
If these two CRC-16 values are the same the slave has received the proper command message.
If these two CRC-16 values are not the same the slave does not respond.
If the command message has a valid slave address, function code, test code, and data value, the
slave will respond with a normal response message. If the command message has an invalid
slave address, function code, test code, and/or data value the slave will respond with a fault
response message.
Command Message
SLAVE ADDRESS
01h
FUNCTION CODE
08h
TEST
00h
UPPER
CODE
00h
LOWER
UPPER A5h
DATA
LOWER 37h
DAh
LOWER
CRC-16
UPPER 8Dh
The Message Format 6-7