Johnson Controls Protocol

The N2 Bus Is a One-Way Street Out

N2 was Johnson Controls' workhorse protocol for decades. Today, it's a migration waiting to happen. We know how to get you out — carefully.

Discuss N2 Migration

What is N2?

N2 is Johnson Controls' proprietary field bus protocol, introduced in the 1980s and used extensively through the 2000s. It connects field controllers (DX-9100, VMA, FX, TEC) to network engines (NAE, NCM).

N2 runs over RS-485 serial at 9600 baud — slow by today's standards, but reliable. The problem isn't performance; it's that nothing new speaks N2.

Modern equipment, analytics platforms, and building systems all expect BACnet or IP connectivity. N2 is an island — and the bridge to the mainland is getting harder to maintain.

N2 Trunk Architecture

RS-485 serial bus, typically up to 100 devices per trunk. Master-slave polling from the NAE/NCM.

Controllers on N2

  • • DX-9100 — Unitary/AHU controllers
  • • VMA — VAV modular assemblies
  • • TEC — Zone thermostats
  • • FX — Field controllers

The Problem

JCI stopped making N2 controllers years ago. Replacements are refurbished or from dwindling stock. The protocol itself has no upgrade path.

N2 Integration Options

N2 Router (JCI)

Johnson Controls' official solution: the N2 Router converts N2 points to BACnet objects. Requires JCI licensing and configuration.

Pros:

  • • Official JCI product
  • • Direct N2-to-BACnet translation
  • • Preserves existing controllers

Cons:

  • • JCI licensing costs
  • • Complex configuration
  • • Availability can be limited
RECOMMENDED

Niagara N2 Driver

Niagara Framework includes an N2 driver that can poll N2 devices directly. No JCI involvement needed. Our preferred approach.

Pros:

  • • Vendor independent
  • • Direct N2 communication
  • • Integrated with Niagara platform

Cons:

  • • Requires Niagara license
  • • Some N2 features may not map

Controller Replacement

Replace N2 controllers with native BACnet equivalents. The cleanest long-term solution, but highest upfront cost.

Pros:

  • • Eliminates N2 entirely
  • • Modern, supported hardware
  • • Full BACnet features

Cons:

  • • Higher capital cost
  • • Requires rewiring in some cases
  • • Programming migration effort

The N2 Migration Reality

Here's what most contractors won't tell you: N2 migration is not straightforward. The protocol is simple, but the programming inside those controllers is often complex and undocumented.

DX-9100 controllers in particular can have extensive custom programming (PCODE) that's been refined over years of operation. Losing that logic means losing building performance.

What We Do Differently

  • Extract programming first — We pull and document PCODE from every DX before any migration
  • Map all points — Complete discovery of every N2 address and what it controls
  • Translate sequences — Convert PCODE logic to Niagara or BACnet controller programming
  • Parallel testing — Run new and old side-by-side before full cutover

N2 Controllers We Work With

DX-9100

The workhorse. Handles AHUs, rooftops, chillers. Complex PCODE programming. Critical to preserve.

VMA (VAV Modular Assembly)

VAV box controllers. High quantity, simpler programming. Good candidates for phased replacement.

FX Series

Field controllers with various I/O configurations. Some have N2, some have BACnet options.

TEC Controllers

Zone thermostats and terminal unit controllers. Often on SA Bus behind a DX or FX.

N2 Migration FAQ

How long can I keep my N2 system running?

With maintenance and access to spare controllers, potentially several more years. But every year the parts get scarcer and expertise harder to find. We recommend starting migration planning now.

Can I migrate one trunk at a time?

Yes, this is often the best approach. We can integrate N2 with Niagara, then replace controllers trunk-by-trunk as budget allows. The building keeps running throughout.

What happens to my schedules and setpoints?

We extract everything from the NAE and controllers before migration. Schedules, setpoints, alarm limits — all transferred to the new system.

Do you need JCI's involvement?

No. We're independent integrators with our own tools and expertise. We can work on N2 systems without going through Johnson Controls — often at lower cost.

Ready to Move Beyond N2?

Whether you need integration now or a migration plan for later — let's talk about your N2 system.

Discuss Your N2 System JCI Upgrades BACnet Migration