BACnet MS/TP to Metasys N2 Data Type Mapping on QuickServer Gateways

When configuring a QuickServer Gateway to bridge data points from BACnet MS/TP to Metasys N2, the most important early step is selecting compatible point data types and ensuring the values are represented correctly on the N2 side. This page provides a reference for mapping commonly used BACnet object types into Metasys N2 point types.

The tables below list (1) the BACnet MS/TP object types commonly encountered during integration, (2) the Metasys N2 point types typically used on the N2 side, and (3) a practical mapping reference showing how each BACnet type is commonly configured when presented as an N2 point through a QuickServer.

Configuration Notes

In practice, BACnet-to-N2 integrations require attention to both the data type mapping and the value semantics. BACnet analog objects typically carry engineering units and may be scaled or limited by the originating device. Metasys N2 points have their own expectations about numeric representation (integer/byte/float) and how values are interpreted by supervisory software.

• Analog values (AI/AO/AV): AI and AO generally map directly to N2 AI/AO. BACnet AV is commonly represented as an N2 float register (ADF) to preserve resolution.
• Binary values (BI/BO/BV): BI and BO generally map directly. BACnet BV is commonly mapped to BD (byte) in N2 configurations, which is often the most compatible representation for “binary value” style points when the N2 side expects a byte-based register.
• Multi-state values (MI/MO/MV): Multi-state input (MI) is typically represented as an integer (ADI) on the N2 side. Multi-state output/value (MO/MV) are often presented as ADF depending on how the target N2 device and the gateway configuration expect to store and expose those values.
• Commissioning validation: After mapping, validate point behavior end-to-end: value updates, commandability (if applicable), and expected value range. For multi-state points, verify that the numeric states (e.g., 1..N) match the site’s documented state text/meaning.

Frequently Asked Questions (FAQ)

Q: Why does BACnet AV map to Metasys N2 ADF instead of AI?

A: BACnet AV (Analog Value) is commonly treated as a general-purpose analog variable and is frequently represented as a floating-point value. Mapping AV to N2 ADF (float register) typically preserves resolution and reduces rounding issues compared to integer-based representations.

Q: What is the difference between Metasys N2 ADI, BD, and ADF?

A: In typical N2 point representations, ADI is used for integer values, BD is used for byte-sized values (often used when a byte/register representation is required), and ADF represents a float register. The correct selection depends on how the gateway is configured and what the N2 supervisory/controller side expects.

Q: How should I map BACnet multi-state objects (MI/MO/MV) to Metasys N2?

A: A common approach is mapping MI (multi-state input) to ADI (integer). For MO and MV, many configurations use ADF to represent the value in a float register format. After mapping, confirm that the state numbers align with the site’s documented state meanings.

Q: Do these mappings guarantee commands will work from Metasys N2 to BACnet MS/TP?

A: No. Data type mapping is necessary but not sufficient. Commandability depends on BACnet object properties (e.g., whether the BACnet object is writable/commandable), gateway role (client/server), and the integration design. Always validate write/command paths in commissioning.

Q: What should I validate after I set up the mappings in the QuickServer?

A: Verify that (1) values update correctly and at the expected rate, (2) analog values are not scaled incorrectly, (3) binary points are not inverted, (4) multi-state points report expected numeric states, and (5) any required commands/write operations function as expected (where supported by the BACnet devices and the gateway configuration).