User Guide

FS-8700-21 LonWorks Manual Page 36 of 62
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Appendix D. SNVT_Type
The following section describes each SNVT as implemented on the FieldServer LonWorks driver.
Data Length – The number of Data Array elements required when specifying a Data Array name under a Map
Descriptor.
Suggested Data Array Formats – This field suggests FieldServer Data Array formats in ascending order of storage
space required while ensuring data integrity. It is not recommended to store a byte value in a bit Data Array since
only the values 0 and 1 will be retained from the byte value resulting in a loss of resolution. If a byte value is
stored in a Floating point Data Array, 3 bytes will go to waste. A SNVT with more than one data item may require a
float Data Array format to prevent loss of resolution. Since FieldServer Map Descriptors can only work with one
type of Data Array format for all the data items in a SNVT, it is sometimes necessary to use a Float Data Array
element for all data items of which some may only have required a Byte. Fortunately, all SNVT’s are short in length
and RAM is adequately provided for on the FieldServer. If a loss in resolution can be tolerated, any Data Array
format may be used.
The range of FieldServer Data Arrays formats are:
Data Array Format
Description
Values Range
BIT
1-bit
0,1
BYTE
8-bit Byte
0.. 255
SINT16
16-bit Signed Integer
-32,768... 32,767
UINT16
16-bit Unsigned Integer
0.. 65,535
SINT32
32-bit Signed Integer
-2,147,483,647... 2,147,483,647
UINT32
32-bit Unsigned Integer
0.. 4,294,967,295
FLOAT
32-bit Float
-3.40282E38... 3.40282E38
Values Range – These are the only values that will be allowed for the SNVT, e.g. a value of 101 will not be
processed in a read or write on SNVT_Switch’s Value data item.
Invalid Value – The Invalid value is used to force the data item’s value should a value outside the value range be
encountered in a read or write. Should the invalid value be N/A ( Not Applicable ), the data item’s value will be
bounded by the indicated values range, e.g. an incoming read value of 101 will be stored as 100 for SNVT_Switch’s
Value data item. Note that in some cases both the type and raw values are specified. Raw values are not of the
same type of the SNVT’s measurement type, i.e. they are not scaled.
Data Item – SNVT’s containing more than one data item have a name specified for each item. This name can be
used in the SNVT_Option field of a Map Descriptor to isolate only this one item.
SNVT_abs_humid
Data Length
1
Suggested Data Array Formats
Float
Data Item 1
Measurement
Units
Values Range
Invalid Value
Absolute humidity
gram/kilogram
0.. 655.34
Raw: 65,535 (0xFFFF)
Type: 655.35
SNVT_address
Data Length
1
Suggested Data Array Formats
Uint16, Float
Data Item 1
Measurement
Units
Values Range
Invalid Value
Neuron Chip Address
16-bit address value
16,384 .. 64,767
N/A