Milltronics ACCUMASS BW500, Instruction Manual

Page: 135 / 141

PL-565 Accumass BW500 Page 135
Communic
a
tions
Error Handling
Modbus Responses
When polled by a Modbus Master, a slave device will do one of the following:
1. Not reply.
Which would mean that something went wrong with the transmission of the message.
2. Echo back the command with the correct response.
This is the normal response. (see the Modbus specifications for more details).
3. Return an Exception Code.
This would reflect an error in the message.
BW500 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
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
04 Slave Device Failure
An unrecoverable error occurred while the slave
was attempting to perform the requested action.
05 Acknowledge
The slave has accepted a request and is
processing it, but a long duration of time is
required.
06 Slave Device Busy
The slave is processing a long-duration program
command
08 Memory Parity Error
The slave attempted to read extended memory,
but detected a parity error in the memory.
Service may be required on the slave
Error Handling
Errors can be divided up into two general sources. Either:
1. There is an error in transmission
2. The user tries to do something that is not a valid action
In the first case, the BW500 will, not respond and let the master wait for a ‘response
time out’ error, which will cause the master to re-send the message.
In the second case, it depends on what the user tries to do. Listed below are various
actions and what the expected outcome is. In general, BW500 will not give an error to
the user request.