Technical Manual
6-36
Exception responses
When the master sends a query to a slave it expects a normal response
(as described earlier). One of the following three events occurs after a query
from the master.
1. Normal response.
The slave has received the query without communication error and can handle
the query normally. The slave returns a normal response.
2. Communication error.
If the slave does not receive the query due to a communication error, or detects
some communication error (parity error or checksum error),
no
response is returned.
The master should process a time-out for the query.
3. Command error.
If the slave receives the query without any communication error, but cannot handle
the query, e.g. if the command was not valid, the requested register number not valid
or instrument in a mode where the command was not allowed, then the slave will
return an exception response informing the master of the nature of the error.
The following exception codes are possible.
Code Name
Description
01
Illegal function
Not a valid function code. Valid function codes are
01, 02, 03, 05, 06, 08, 15, 16.
02
Illegal data address
Not a valid data address. See ‘Register description’
for a list of allowed registers.
03
Illegal data value
Value in data query field not valid. To get a better
explanation of the error, the ‘command error’ register
could be read.
07
Negative
acknowledgement
The instrument has received the query but cannot
perform it.
To get a better explanation of the error,
the ‘command error’ register could be read.
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