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CONNECTING MULTIPLE LMCP PANELS IN A NETWORK
The LMCP can connect to other LMCP panels via BACnet, using the MS/TP connections. Connecting panels to each other
via BACnet allows them to share common group numbers for schedules or switches. This provides the ability to program a
common behavior for an entire building or section of a building, via LMCS-100 software
One or more LMCPs can also be connected to other devices in a Building Automation System (BAS) using BACnet. This
provides for connection to a Segment Manager or other supervisory system. The BACnet settings can be configured using the
LMCT-100 controller or LMCS-100 software.
BACnet Settings
The following parameter settings and concepts are important to understand when configuring the LMCP for BACnet
communication:
• Device ID – The device ID is a unique number, between 0 and 4194302, that identifies a device in a BACnet network.
Every device in the network must have a different number. By default, the LMCP uses the last 6 digits of the serial number
(plus a leading 0 to complete the seven digit number). This number can be changed if needed, for example, when required
by an integrator, as part of a BAS. Once set, the LMCP will remember the ID number even if other parameters are reset to
their default values.
• Device Name – This is a label for the panel, useful when working with LMCS in a situation where multiple panels are
used, to help more easily distinguish between the panels. Any numerals or letters can be used in naming the panel. By
default, the name is the same as the serial number. The name can be programmed using either LMCS, the LMCT-100, or
a BAS application.
• MS/TP MAC Address – The MS/TP MAC address is an additional identifier, used by the devices on the network to
communicate with each other. It is a number between 0 and 127. It is important to understand the difference between the
device ID and the MS/TP MAC Address. The Device ID is, in essence, a number that identifies “who” the devices is, while
the MS/TP MAC address identifies its “location”.
In a BACnet network, all the devices pass a token to each other to determine which device has control of communication
over the network. The MS/TP MAC address is used to “locate” other devices. When a device receives the token, it will
take control of the communication and send messages to other devices as needed. It then passes the token to the
device with the next highest MS/TP MAC address. In order to do this, it sends an “Are you there?” message on the MAC
address one higher than its own. If it receives a response, it passes the token. If it does not receive a response, it tries
again on the next highest number, continuing in this manner until it receives a response. This “Are you there?” message
is referred to as a Poll For Master.
NOTE: In order to send and respond to this Poll For Master message, a device must be designated as a master device.
Other devices (slave devices) on the network will not respond, and cannot take control of the communication.
While the Device ID is fixed and should not change, the MS/TP MAC address can change as devices come on or drop off
the network. By default, the LMCP will automatically assign an MS/TP MAC address. When the LMCP is powered up, it
will check the network for other devices to determine if its current MAC address is being used by another device. If, not it
will keep the same address, but if it is, and will assign an unused number between 32 and 127.
You can manually assign an MS/TP MAC address instead of having the LMCP automatically assign the number. This can
be useful, especially in larger networks where response time is important. Since the Poll For Master message checks the
next highest address number and then increments that number until it finds a device, having devices with gaps between
numbers can increase latency. If you have 10 devices, numbered 0–9, you will have optimal performance since no time is
wasted sending the Poll For Master message to an unused number.
• Max Master – The Max Master parameter is another parameter that will cut down on latency. The value you set for this
parameter is the highest number the LMCP will check when sending a Poll For Master message, before returning to 0.
So, in the previous example, where there are 10 devices numbered 0–9, if you set the Max Master to 9, it will never check
addresses 10–127.
NOTE: If using the LMCP with a global controller such as a router, BAS or Segment Manager, the global controller will
always default to a MAC address of 0.
NOTE: You should be aware that devices connected over the DLM Local Network also have MAC addresses for
communication purposes, but that MAC address is entirely separate from the MS/TP MAC address.
Further details on Device IDs and MAC addresses can be found in WattStopper’s Technical Bulletin #180 at http://www.
wattstopper.com/resources/download-center/tech-bulletins-whitepapers.aspx.
Examples of Using the LMCP in a BACnet Network
The following three examples demonstrate applications for connecting the LMCP to a BACnet network:
Two or more LMCP panels connected to each other without a Segment Manager or BAS
This is the simplest configuration. Remember that when a relay is assigned to a group, if more than one panel uses the same
group number, those relays in the different panels will respond to any events or controllers that affect that group. While this can
provide an easy way of controlling relays in multiple locations, if that is not what you want, make sure to use different group
numbers in different panels.
When connecting the panels via the MS/TP jack, keep in mind that the general rules for BACnet MS/TP apply. This includes
termination quality, polarity of the dataline, maximum network physical length, usage of repeaters/isolators, usage of proper
dataline (LM-MSTP and LM-MSTP-DB only), etc.
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