Local FC Bus rules and specifications - Metasys - LIT-12011034 - General System Information - Metasys System - Release 11.0

MS/TP Communications Bus Technical Bulletin

Brand
Metasys
Product name
Metasys System
Document type
Technical Bulletin
Document number
LIT-12011034
Version
Release 11.0
Revision date
2022-02-07
Language
English

Table 1, Table 2, and Figure 1 provide rules and specifications for the local FC bus. (For the Remote Field Bus, see Table 1.) Metasys MS/TP devices generate less data traffic than third-party MS/TP devices and TEC26xx thermostats. Connecting third-party devices or TEC26xx Series thermostats to the FC bus increases data traffic, reduces bus performance, and reduces the number of devices that can be connected to the FC bus.

Table 1. Local FC Bus rules and limitations

Category

Rules/limits

General

NAE55 Series models can support up to two local FC buses.

Note: When a second FC bus is added to the NAE, be sure the trunk number has not been used on the NAE and enter a Network Address that is unique for the entire site. This applies for any model of NAE.

NAE45 Series models can support one local FC bus.

NAE35 Series models can support one local FC bus (but an NAE35 FC bus supports only half the number of devices that are supported on an FC bus on an NAE45 or NAE55).

NCE25 Series models can support one local FC bus. NCEs must be ordered specifically as N2 or MS/TP models.

NAE85 / OAS / ODS do not support local FC bus. See Table 1 for the Remote Field Bus specifications.

SNE22xxx Series models can support two local FC bus.

SNE11xxx Series models can support one local FC bus.

SNE105xx Series models can support one local FC bus.

SNC2515x-0x Series models can support one local FC bus.

SNC1612x-0x Series models can support one local FC bus.

Note: BACnet MS/TP only supports the daisy chain configuration.

Refer to the Network Engines Product Bulletin (LIT-12012138) and the Network Controller Engine Product Bulletin for complete information on MS/TP bus support on NAE/NCE/SNC/SNE models.

Number of devices and Bus segments

NCE25 models support 32 MS/TP devices (maximum) on an FC bus trunk and up to 3 bus segments.

NAE35 models support the following device limits on an FC bus trunk:

When all of the devices connected on the FC bus are Metasys devices or non-Metasys devices such as the PK-OEM, ATC, VAC, VEC, and ZEC, the d evice and bus segment limits are as follows:

  • 50 devices total per FC bus (maximum)
  • 3 bus segments per FC bus (maximum)
When one or more non-FEC family device is connected on the FC bus, the device and bus segment limits are as follows:
  • 32 devices total per FC bus (maximum)
  • 3 bus segments per FC bus (maximum)

NAE45 and NAE55 models support the following device limits on an FC bus trunk:

When all of the devices connected on the FC bus are Metasys devices or non-Metasys devices such as PK-OEM, ATC, VAC, VEC, and ZEC, the d evice and bus segment limits are as follows:

  • 100 devices total per FC bus (maximum)
  • 3 bus segments per FC bus (maximum)
  • 50 devices per bus segment (maximum, not to exceed 100 devices per FC bus)
When one or more non-FEC family device is connected on the FC bus, the device and bus segment limits are as follows:
  • 64 devices total per FC bus (maximum)
  • 3 bus segments per FC bus (maximum)
  • 32 devices per bus segment (maximum, not to exceed 64 devices per FC bus)

When one or more non-FEC family device is connected on the FC bus, the device and bus segment limits are as follows:

SNE22xxx models support the following device limits on an FC bus trunk: 64

SNE11xxx models support the following device limits on an FC bus trunk: 64

SNE105xx models support the following device limits on an FC bus trunk: 32

SNC2515x-0x models support the following device limits on an FC bus trunk: 32

SNC1612x-0x models support the following device limits on an FC bus trunk: 32

Bus segments on an FC bus are connected with repeaters (only). Up to two cascaded repeaters may be applied to an FC bus (to connect three bus segments).

Cable length for FC Bus and Bus segments

When all of the devices connected on the FC bus are Metasys devices the cable length limits (using 22 AWG 3-wire twisted, shielded cable) are as follows:
  • Each bus segment can be up to 1,520 m (5,000 ft) in length.
  • Each FC bus can be up to 4,570 m (15,000 ft) in length.
When one or more non-FEC family or third-party MS/TP device is connected on the FC bus, the device and bus segment limits are as follows:
  • Each bus segment can be up to 1,220 m (4,000 ft) in length.
  • Each FC bus can be up to 3,660 m (12,000 ft) in length.
Note: Do not place subordinate devices on the FC bus. Subordinate devices on the FC bus are not supported.

When using fiber-optic connections: 2,010 m (6,600 ft) between two fiber modems.

Recommended cable

22 AWG Stranded, 3-Wire Twisted, Shielded Cable

EOL termination

The EOL switch must be set to On (or an EOL terminator installed) on the two devices located at either end of each bus segment on an FC bus. The EOL switches must be set to Off (or EOL termination disabled) for all other devices on the bus segment on an FC bus. See End-of-line termination on local FC Bus for more information.

Notes:
  • The recommended cable type provides the best bus performance. See MS/TP Bus cable recommendations for information on alternative cable types and lengths that may be used in MS/TP applications.
  • If third-party devices are connected to the bus, the cable lengths should be reduced (if necessary) to match the third-party vendor recommendations.
Figure 1. FC Bus with three Bus segments connected with repeaters
Note: When third party MS/TP devices are connected to an FC Bus, a bus segment supports only up to 32 devices and the FC Bus supports only up to 64 devices.
Note: For optimum noise protection the location with G are the ideal shield grounding locations. This provides one shield ground per bus segment, grounding at the source of the bus for that segment. It is also acceptable to ground the shield only at the SNE if the shields are made continuous across repeaters side A and B; however; the noise protection is somewhat less with the wiring configuration.
Note: While each bus segment can support up to 50 Metasys Device connections, the total on the FC Bus cannot exceed 100, including the SNE.

The bus segments on an FC bus are connected using repeaters (only). A repeater has two device connections, which are independent of each other. Each device connection on the repeater is connected to a bus segment just like any other device connection on the segment, and a repeater device connection can be connected at the end of a bus segment or anywhere along the segment. When a repeater device connection is at the end of a bus segment, EOL termination must be enabled on that repeater device connection. See Figure 1 for more examples of repeaters on FC buses.

Table 2. FC Bus specifications

Category

Specification

Error checking

Message Headers checked using 8-bit Cyclic Redundancy Check (CRC) test. Message data check using 16-bit CRC test.

Device addressing

0–255 (See Device addressing on the MS/TP Bus for more information.)

Data transmission standard

RS485

Signaling method

BACnet® MS/TP

Signaling rate

9600; 19,200; 38,400; or 76,800 baud as selected by bus supervisor. (See Baud rates on the MS/TP Bus.)

Transient immunity

Meets EN61000-4-4 and EN6100-4-5 requirements for heavy industrial applications.

Protected against misapplication of 24 VAC.

EOL termination method

Integral EOL Termination switch or add-on EOL Terminator module (See End-of-line termination on local FC Bus.) Do not use third-party EOL termination.

Shield grounding

Only one hard ground connection per bus segment when using shielded cable. (See Grounding the MS/TP Bus cable shield.)

Physical configuration

Daisy-chained

Optional vendor components

Repeaters
  • Acromag® 4683-TTM-1F (115 VAC)

  • Acromag 4683-TTM-2F (230 VAC)

  • Acromag 4683-TTM-3F (24 VAC)
Note: A repeater is required to support more than 32 devices per trunk segment or trunk cable segment longer than 1,220 m (4,000 ft). Only the repeaters listed here provide EOL termination switching that is compatible with MS/TP.

Transient eliminator

For further information, see Surge protectors.

Fiber modem
  • S.I. Tech Model 2110BAC Fiber-Optic Modem and S.I. Tech 2121 Power Supply

  • 9-pin Male Connector Kit (required by 2110BAC modem)
  • Does not support 76,800 baud
Note: A DIN rail mounting version of the Model 2110BAC may be available as Model 2110BAC-DIN. However it does not appear on the S.I. Tech web site at the time of this writing. Contact S.I. Tech using contact information on their web site at http://www.sitech-bitdriver.com/index.htm.