CRC1/CRC1+ BACnet® MS/TP Application Guide
LG ELECTRONICS U.S.A., INC.
Air Conditioning Technologies
4300 North Point Parkway
Alpharetta, GA 30022
The BACnet MS/TP (Master Slave/Token Passing) driver implements a data link protocol that uses the services of the RS-485 physical layer on a shielded twisted pair cable. BACnet MS/TP is typically used for connecting field devices to controllers, routers, and/or control applications (i.e., the LG MultiSITE VM3).
The BACnet MS/TP capability included with the CRC allows for direct and seamless integration to third-party Building Management Systems (BMS), where BACnet MS/TP is utilized. For example, a data closet being served by an LG system with a CRC can be added to an existing building with a BMS. The most efficient way to integrate the LG System would be via the CRC over BACnet MS/TP directly to the BMS.
Figure 1 Description: A diagram illustrating the integration of an LG system, featuring a CRC and remote controllers connected via a Remote Controller Bus, into a Building Management System (BMS) using the BACnet MS/TP protocol. This setup allows for direct and seamless data exchange.
In addition to new construction projects, the CRC is ideal for small additions to existing buildings. The CRC is compatible with all LG Multi V, Multi V S, and Multi F systems.
Communication Network Wiring Specifications
CRC BACnet MS/TP communication wiring requires AWG 18, two-core (18/2) stranded, twisted, and shielded communication cable.
Communication Network Design Considerations
A BACnet MS/TP network (including CRC and other BACnet MS/TP devices) has requirements on network design. Below are some guidelines to follow when designing the BACnet MS/TP network including the CRC as well as other BACnet MS/TP devices:
- Maximum length per MSTP Segment: 3900'
- 64 CRCs per MSTP Segment
- End-of-Line (EOL) Resistors: 120 ohm resistors must be installed at each end of the MSTP (or RS-485) trunk segment to reduce signal reflections and RF interference. Failure to install EOL resistors may result in intermittent communications errors.
Communication Network Wiring
The BACnet MS/TP communication cable connects to terminals 13 and 14 on the terminal strip on the CRC. NOTE: Connect shields together and insulate to prevent accidental grounding. Daisy chain the CRC onto the BACnet MS/TP communication bus with other CRCs and/or other BACnet MS/TP devices.
Figure 2 Description: A diagram depicting the terminal connections on the back of a CRC, showing terminals for power (12VDC, Common) and BACnet communication (BACnet+, BACnet-, BACnet Common), along with unused ports. It also illustrates the daisy-chain configuration of multiple CRCs and remote controllers on the BACnet MS/TP communication bus.
Communication Network Installation Considerations
One of the most common causes of communication failures within a BACnet MS/TP Communication Network is related to network installation, i.e., improper wiring installation. The below list highlights some good practices to ensure correct installs:
- Polarity sensitive.
- Never splice.
- Avoid unwinding the twists of cable when not necessary. Twisting the insulated conductors around each other reduces outward noise and improves immunity to external noise pickup. Twist the two wires together before inserting them into the corresponding screw terminal of the controller.
- Avoid exposing too much bare wire so that adjacent wires do not short when connected to the controller.
- Avoid running network cables near DC signal switches, variable frequency drives, and high voltage cabling to prevent introduction of noise.
- Secure the network cables to reduce vibration as much as possible.
Integrating the CRC's over BACnet MS/TP offers additional points allowing for remote screen configuration and ZigBee device configuration.
Device Parameters
| Name | Type | Read/Write | BACnet Object ID | Device Facets |
|---|---|---|---|---|
| ZB_Snsr_Wn_Interlock_M | Binary Value | Read | 552 | Window Interlock Deactivated, Window Interlock Activated |
| MsgShortScreenMsgTxt | characterStringValue | Write | 1 | N/A |
| MsgLongScreenMsgTxt | characterStringValue | Write | 2 | N/A |
| ZB_Zone1IEEEaddrs_M | Analog Input | Read | 210 | N/A |
| ConfigPassword | Analog Value | Write | 56 | N/A |
| BACnetComAddr | Analog Value | Write | 10 | N/A |
| BACnet Stack Poll Rate | Analog Value | Write | 16 | N/A |
| DisplayLowBacklight | Analog Value | Write | 3 | N/A |
| UserPassword | Analog Value | Write | 57 | N/A |
| ZB_NetworkStatus_M | Multi State Input | Read | 2 | Not Det = 1, Pwr On = 2, No NWK = 3, Joined = 4, Online = 5 |
| ZB_Zone1Status_M | Multi State Input | Read | 210 | None = 1, Closed = 2, Opened = 3, No Motion = 4, |
| DisplayLanguage | Multi State Value | Write | 4 | English = 1, French = 2, Spanish = 3 |
| BACnetNetworkUnits | Multi State Value | Write | 6 | SI = 1, Imperial = 2 |
| DisplayTimeFormat | Multi State Value | Write | 5 | AM/PM = 1, 24Hours = 2 |
| DisplayColor | Multi State Value | Write | 2 | White = 1, Green = 2, Blue = 3, Grey = 4, Dark Grey = 5 |
| DisplayUseStandbyScreen | Multi State Value | Write | 32 | No = 1, Yes = 2, Occ Only = 3, Screen = 4 |
| ZB_Zone1SnsrType | Multi State Value | Write | 210 | None = 1, Window = 2, Door = 3, Motion = 4, Status = 5, Remove = 6, N/A = 7 |
| DisplayShowOnOff | Multi State Value | Write | 500 | Show = 1, Hide = 2 |
| DisplayShowMode | Multi State Value | Write | 501 | Show = 1, Hide = 2 |
| DisplayShowSchedule | Multi State Value | Write | 502 | Show = 1, Hide = 2 |
| DisplayShowMore | Multi State Value | Write | 503 | Show = 1, Hide = 2 |
| DisplayShowSetTemp | Multi State Value | Write | 504 | Show = 1, Hide = 2 |
| DisplayShowSpaceTemp | Multi State Value | Write | 505 | Show = 1, Hide = 2 |
| DisplayShowFanSpeed | Multi State Value | Write | 506 | Show = 1, Hide = 2 |
| DisplayShowHumidity | Multi State Value | Write | 507 | Show = 1, Hide = 2 |
| TempSenseLoc | Multi State Value | Write | 516 | Remote Controller = 1, IDU = 2, 2TH = 3 |
Additional documentation including a complete points list can be found at www.lghvac.com.
*BACnet is a registered trademark of ASHRAE.
