Metasys N2 - Knowledge Base

What Metasys N2 Is

Metasys N2 is a proprietary serial protocol developed by Johnson Controls for building automation controllers. It is commonly encountered when integrating legacy Johnson Controls equipment into modern BACnet or Modbus supervisory systems via a protocol gateway. N2 communicates over RS-485 at 9600 baud (default).

Core Concepts

Concept	Description
N2 Bus	RS-485 serial bus connecting controllers to a supervisory device
Device Address	Sequential node address on the N2 bus (typically 11–18 for VAVs)
Point Count	Number of data points per device — varies by device type
AV Mapping	N2 data maps to BACnet Analog Value (AV) objects; binary N2 data does not map cleanly to BACnet Binary types
VMA Node_Type	Required field for N2Open configurations — identifies the device profile

Protocol Variants

Variant	Use Case	Key Difference
Standard N2	Straightforward serial integration	Simple addressing and point mapping
N2Open	Extended controllers with VMA profiles	Requires VMA Node_Type field in configuration
Facility Explorer	Johnson Controls FX series	Different configuration requirements than Standard N2 or N2Open

[!WARNING] The #1 recurring support issue is N2 variant misidentification. Standard N2, N2Open, and Facility Explorer each require different gateway configurations. A single intake question prevents a full configuration rework.

Common Device Point Counts

Device Type	Typical Points	Notes
VAV Type A	77	Largest point count per unit
VAV Type B	56	Mid-range
VAV Type C	38	Smallest

[!NOTE] Mixed VAV installations require one configuration per device type, not a single consolidated config. Calculate total point counts across all device types to validate the gateway’s point count tier (250 / 500 / 1000) before deployment.

Integration Prerequisites

1. Confirm the N2 variant — Standard N2, N2Open, or Facility Explorer.
2. Collect all bus addresses before configuration starts.
3. Identify device types and point counts for each address.
4. VMA Node_Type (if N2Open) — required for correct driver mapping.
5. Validate point count tier — total points across all devices must fit within the gateway tier.

Common Problems

• Variant misidentification — assuming Standard N2 when the site uses N2Open or Facility Explorer requires a complete configuration rebuild.
• Point count tier exceeded — a 500-point tier is insufficient for 8+ device installations (e.g., 522 total points). Validate at time of sale.
• Mixed VAV types treated as one config — each device type (77/56/38 points) needs a separate configuration section.
• N2 timeout errors during commissioning — typically caused by wiring, termination, or addressing issues, not configuration errors.
• Post-deployment scaling errors — data accuracy issues after long gaps between configuration and commissioning.

Tools & Diagnostics

Tool	Type	Description
System Configuration Tool (SCT)	Configuration	Johnson Controls’ proprietary tool for configuring Metasys N2 controllers and programming VMA devices.
Metasys Launcher	Management	Central management UI for Metasys BMS systems — device browsing, point inspection, and scheduling.

Related Pages

• BACnet - Knowledge Base
• BACnet Objects & Properties Reference
• Protocol Conversion - Knowledge Base
• QuickServer - Knowledge Base
• Gateway - Knowledge Base