Table of Contents
Error Handling
Modbus Responses
When polled by a Modbus Master, a slave device will do one of the following:
1.
Not reply. This means that something went wrong with the transmission of the
message.
2.
Echo back the command with the correct response (see the Modbus specification
for more details). This is the normal response.
3.
Return an Exception Code. This reflects an error in the message.
HydroRanger 200 uses the following exception codes:
Code
01
Illegal Function
02
Illegal Data Address
03
Illegal Data Value
Error Handling
Errors can be traced to two general sources:
1.
There is an error in transmission.
OR
2.
The host tries to do something that is not a valid action.
In the first case, the HydroRanger 200 does not respond and the master waits for a
response time out error, which causes the master to re-send the message.
In the second case, the response depends on what the host tries to do. In general,
HydroRanger 200 will not give an error to the host request. Various actions and the
expected outcome are as follows:
•
If the host reads an invalid register, the host will get an undetermined value back.
•
If the host writes an invalid register (a non-existing parameter or a read only
parameter), the value will be ignored and no error response will be made. However,
the current value will not reflect the desired new value.
•
If the host writes a read only register, then the value will be ignored and no error
response will be made. However, the current value will not reflect the desired new
value.
•
If P000 is activated, then the value will be ignored and no error response will be
made. However, the current value will not reflect the desired new value.
7ML19985FC03
Name
HydroRanger 200 – INSTRUCTION MANUAL
Meaning
The function code received in the query is
not an allowable action for the slave.
The data address received in the query is
not an allowable address for the slave.
A value contained in the query data field
is not an allowable value for the slave.
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