July 2012

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BACnet Testing Laboratories

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BACnet-N2 Router

System-91 Integration Enhancements

Steve Jones
Steven E Jones
Managing Partner,
The S4 Group, Inc

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Our original implementation of the S4 Open Appliances included support for all MetasysŪ N2 devices. The N2 Router design followed the various N2 protocol specifications available. N2 is actually a series of sub-protocols co-existing on the same serial bus, sharing a common framing and a common addressing strategy. Within the data frames, the N2 Open, VMA (N2B), and System-91 protocols are completely separate and unique implementations. The N2 Open and N2B standards are unique-- but share a common trait in that they reflect the data organization and user experience that a MetasysŪ operator would have from the MetasysŪ Operator Workstation.

Over the last several months, we have discussed upcoming enhancements to the BACnet-N2 Router. These enhancements are now undergoing field-testing.

Details of the enhancements follow.

1.    Override and Release Emulation for System91 Devices
The System-91 family is drastically different from N2 Open devices in many ways. One of the most significant is that the System-91 designers did not follow the Override and Release mechanisms of N2 Open devices. Instead, modules in System-91 devices are placed in either Auto or Hold mode. Hold mode disconnects the module output from the algorithm and allows you to write a desired value to the output points. However, when natively working with the DX-9100, it takes a three-step process to achieve this result.

Many BACnet Operator Workstations and controllers do not have the flexibility to implement this multi-step process. With this enhancement, the S4 Open appliances take care of the details in the background. You simply add the .Override or .Release attribute to point source strings to allow you to Override a point or Release it back to normal operation exactly as you do with N2 Open devices. In this S4 open Appliance release, Override and Release are supported for the DX-9100 controller. Future efforts will extend this capability to other System-91 devices, as the marketplace requires.

2.    Publishing to Specific BACnet Data Object Types
Our original implementation of the S4 Open Appliances published all DX-9100 points as BACnet AV or BV points. With this enhancement, System-91 data objects are published to appropriate BACnet data objects as BI, BO, AI, AO, AV, or BV points. In addition, this capability is extended to N2 Open and VMA devices to give the integrator complete control over how points are published to BACnet.

3.    Shortened N2 Device and Point Names
Through our work with integration partners who were utilizing different BACnet implementations, we found that in our initial effort to provide user-friendly point names, we inadvertantly created BACnet Object Names that were too long for some of the BACnet implementations. As part of this enhancement package, we edited all device type templates in the catalog and eliminated unnecessary words, abbreviated common words or phrases, and aimed to approach consistency in abbreviations used.


As soon as field-testing completes, these enhancements will be released as the next production version of the S4 Open Appliances. Existing customers with active Software Assurance agreements will be eligible for free upgrades.

These enhancements continue our efforts to free our integration partners from the details and idiosyncrasies of MetasysŪ systems and provide consistent interfaces and functions for all N2 devices, independently of what MetasysŪ product family or generation they belong to. The ultimate goal is to provide our partners with power and control without complexity. Simplifying the way you interact with the System-91 line of N2 devices is a major step in this direction.


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