6-6 The Message Format
Fault Response Message
The fault response message contains the same slave address as the command message,
indicating to the master which slave is responding.
The function code of a fault response message is actually a value of 80h plus the original function
code of 03h. This indicates to the master that the message is a fault response message, instead
of a normal response message.
The error code indicates where the error occurred in the command message. The value of 2h in
the error code field of this fault response message, indicates that the command message
requested data be read from an invalid register. A complete listing of the error codes is shown in
Chapter 8, Troubleshooting and Error Codes.
A CRC-16 value is generated from a calculation using the values of the address, function code,
and error code sections of the message. The procedure for calculating a CRC-16 value is
described at the end of this chapter. How the response message is handled by the master
depends on what master is used. When the master receives the fault response message it
should calculate a CRC-16 value and compare it to the one in the CRC-16 field of the fault
response message. If these two CRC-16 values are the same the master has received the
proper fault response message.
02h
SLAVE ADDRESS
80h + FUNC. CODE
83h
02h
30h
F1h
CRC-16
LOWER
UPPER
ERROR CODE
Summary of Contents for GPD 515/G5 Modbus RTU
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Page 24: ...6 4 The Message Format ...
Page 30: ...6 10 The Message Format ...
