Network engine configuration for adding Remote Field Bus - Metasys - LIT-12011034 - General System Information - Metasys System - Release 11.0

MS/TP Communications Bus Technical Bulletin

Product name
Metasys System
Document type
Technical Bulletin
Document number
Release 11.0
Revision date

You define the Remote Field Bus at a Metasys network engine much like you define a local field bus. Important settings include Trunk Number and Network Address.

Trunk number

On a network engine, trunk numbers 1 and 2 are reserved for the local field bus integration. Trunk numbers 3 to 20 are reserved for Remote Field Bus integrations. The quantity of field buses supported on any particular device varies according to the specific device in use. Generally, the number of supported trunks is less than the maximum trunk number allowed (Table 1). For example, an OAS supports 16 field buses maximum, not 20 field buses as the trunk number range would suggest. If the specific device does not support a local field bus, start with trunk 3, as trunk numbers 1 and 2 are not supported.

Network address

The network address you specify for a Remote Field Bus integration must match the BACnet Router MS/TP-side network number you specify. The network address must be unique at the site. Keep in mind that each MS/TP trunk on each SNE has a network number that needs to be considered when determining a unique ID. This address is used to locate and establish communication between the Remote Field Bus and the router. A defined Remote Field Bus can only work with one router. If you need to change the network address of a Remote Field Bus after it has been configured, you must restart the Metasys network engine to complete the re-configuration.

Number of Field Buses allowed

The total number of local and remote field buses allowed depends on the type of controller as outlined in Table 1. For example, an NIE55 can have up to eight field buses, but an NCE25 or NIE29 can only support one local field bus and no remote field bus.

Table 1. Maximum number of Field Buses per controller
Controller Maximum number of Field Buses (local and remote)
OAS 18 remote field bus only
SNE2200x-0 8
SNE110Lx-0 1
SNE1050x-0 / SNE1100x-0 4
SNC2515x-0x 3 remote field bus and 1 local field bus
SNC1612x-0x 3 remote field bus and 1 local field bus
NAE85 / NIE89 16
NAE55 / NIE59 8
NAE35 / NAE45 / NIE39 / NIE49 4
NCE25 / NIE29 1 (local field bus only; remote field bus not supported)
ODS 16
Note: The SNC requires Release 11.0 or higher to support the Remote Field Bus integration.
Note: The Remote Field Bus supports up to 32 field devices per BACnet Router on a bus with all Johnson Controls devices, or up to 16 field devices on a bus with a mix of Johnson Controls and third-party devices. Limitations are listed in the Metasys System Configuration Guide (LIT-12011832). Also, to take advantage of bus diagnostics, at least one Johnson Controls field device is required on the Remote Field Bus.

Configuration attributes only for Local Field Bus

If the same field bus configuration attribute is specified at both the BACnet Router and the Remote Field Bus, the attribute setting on the BACnet Router prevails. For example, if a Baud Rate of 38400 is specified at the BACnet Router but a Baud Rate of 76800 is specified on the Remote Field Bus, 38400 is used as the Baud Rate on the bus. To be consistent, we recommend that you match the Remote Field Bus attribute values with that of the router, or you can keep the default values at the Metasys network engine. See BACnet router configuration for a partial attribute list.