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FS-8700-19_Metasys_N2 Driver Manual Page 10 of 51
FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web:www.fieldserver.com
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N2Open Attribute Table
Data Type Attribute No. Attribute
1
Object Configuration
2
Object Status
3
Analog Input Value
4
Low Alarm Limit
5
High Alarm Limit
6
Low Warn Limit
7
High Warn Limit
Analog Input
8
Differential
1
Object Configuration
Binary Input
2
Object Status
1
Object Configuration
2
Object Status
Analog Output
3
Current Value
1
Object Configuration
2
Object Status
3
Minimum On-Time
4
Minimum Off-Time
Binary Output
5
Maximum Cycles/Hour
1
Object Status
Internal Float
2
Current Value
1
Object Status
Internal Integer
2
Current Value
1
Object Status
Internal Byte
2
Current Value
Using Change of State (COS) – N2Open
If a large number of points are to be monitored, optimal efficiency is achieved by
using the COS mechanism instead of reading each individual point directly. A
N2Open device responds to a COS poll with a change record if a change has taken
place. On startup the device will report the state of all its points when it receives a
COS poll.
Two kinds of Map Descriptors are required for every node that is to be monitored
using COS:
A COS polling Map Descriptor with Function set to COS_Poll.
A COS_Read (i.e. Function set to COS_Read) Map Descriptor for every point
on that node that is to be monitored. Any COS records received will be stored to
the matching Map Descriptor data location.
Note that the COS_Read Map Descriptor has an optional scan_interval. If a value is
set the Map Descriptor will poll at that rate in addition to receiving COS data. This
can be used if the values are to be refreshed continually even if they don’t change. If
the scan_interval is not configured (through omitting the column, or by setting the
value to ‘-‘) the COS_Read Map Descriptor will not cause active polls once the value
has been initialized. See 4.4.4 for example.
Important Note on COS Operation in N2Open
Please be aware that N2Open devices will only report value changes under the
following conditions: