Siemens 200 instruction manual Error Handling, Modbus Responses, Code Name Meaning

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. MultiRanger uses the following exception codes:

Code	Name	Meaning
01	Illegal Function	The function code received in the query is
		not an allowable action for the slave.
02	Illegal Data Address	The data address received in the query is
		not an allowable address for the slave.
03	Illegal Data Value	A value contained in the query data field
		is not an allowable value for the slave.

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 MultiRanger 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, MultiRanger 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.

7ML19981FB06 MultiRanger 100/200 – INSTRUCTION MANUAL Page 111

Error Handling