Thermo Scientific AquaSensors
™
DataStick
™
Ethernet Communications User Guide
48
6.5.7.3
Common Services
Implemented for
Service Code
Class Level
Instance Level
Service Name
0E
HEX
Yes Yes Get_Attribute_Single
6.5.8 System Status Object (64
HEX
– 1 Instance)
When power is applied to the Ethernet product, it takes a short amount of time for it to
update its local copy of the data stored in the DataStick Body. The Data Valid attribute
can be used to determine when this operation is complete. It changes from 0 to 1 when
the local copy of the data has been completely updated.
The Ethernet product provides access to data stored in the product itself as well as data
stored in the Data Stick Body. When data stored in the product itself is accessed, the
success or failure of the operation is indicated immediately. When data stored in the
DataStick Body is accessed, the immediate indication is success even though the overall
operation may have failed. This is because the protocol being used doesn’t tolerate the
kind of delays necessary to accomplish an access of this type. To assist the programmer
in determining the overall success or failure of accessing DataStick Body data, four
counter attributes are available:
1.
Writes Pending
2.
Read Error Count
3.
Write Error Count
4.
Timeout Count
The Writes Pending is incremented every time the Ethernet product has been asked to
write to the DataStick but has not yet completed the operation. The count is decremented
each time a write completes.
The Read Error Count is incremented every time the Ethernet product receives an error
while trying to read from the DataStick Body. It is a count of the total number of read
errors for all of the protocols supported. Some DataStick Body data might not be
available depending on the type of Sensor Head installed. When the Ethernet product
tries to read this unavailable data the DataStick will respond with an error and this will
cause the Read Error Count to be incremented. The Ethernet product will realize that this
data is unavailable and stop requesting it.
The Write Error Count is incremented every time the Ethernet product receives an error
while trying to write to the DataStick. It is a count of the total number of write errors for
all of the protocols supported. For instance, if an attempt is made to change the Sensor
Filter value to 200, the DataStick will respond with an error because the largest
acceptable value is 100 and this will cause the Write Error Counter to be incremented.
The Timeout Count is incremented every time the Ethernet product fails to receive a
response from the DataStick in a reasonable amount of time. It is a count of the total
number of write errors for all of the protocols supported.
The counters can be cleared to 0 by setting them to 0.
