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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 | 0,1 | |
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BYTE | 0.. 255 | |
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SINT16 | ||
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UINT16 | 0.. 65,535 | |
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SINT32 | ||
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UINT32 | 0.. 4,294,967,295 | |
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FLOAT | ||
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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.
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| Data Length |
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| 1 |
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| Suggested Data Array Formats |
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| Float |
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| SNVT_abs_humid |
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| Data Item 1 |
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| Measurement |
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| Absolute humidity |
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| gram/kilogram |
| 0.. 655.34 |
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| Raw: 65,535 (0xFFFF) |
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| Type: 655.35 |
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| Data Length |
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| 1 |
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| Uint16, Float |
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| SNVT_address |
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| Data Item 1 |
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| Measurement |
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| Values Range |
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| Invalid Value |
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| Neuron Chip Address |
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| 16,384 .. 64,767 |
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| N/A |
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FieldServer Technologies 1991 Tarob Court Milpitas, California 95035 USA Web: www.fieldserver.com Tel: (408) 262 2299 Fax: (408) 262 2269 Toll Free: (888) 509 1970 email: support@fieldserver.com
