LC&D - Unstable Bus Characteristics


When do you have an ‘Unstable Bus’?


  • When your Grouped relays are not turning on/off at the right times.
  • When your Display doesn’t appear to be on.
  • When your Display keeps changing from one screen to another, when numerous options are being highlighted. As if the buttons are being pressed by themselves.



  1. Bus Scan Display:

Screen where a summary of the bus is displayed.


Each numerical position on the screen represents an item on the bus. There

are 127 locations for these items. The clock is always at address Zero to

make 128 items.

Each 3 represents an 8 relay card or part of a Relay card,

Each 1 represents a photocell or switch or a DigiLink.


This screen is considered to be a “PRESENCE MAP” of the system and shows what is present and what is not.


Bus Scan Display Picture:


  1. Unstable Bus

When the Bus Scan Display is has continuous compiling errors, as shown in the picture below


The 1st number (to the left of the dash) counts device drop offs. If a device on the bus doesn’t answer 3 times, it will be labeled as a missing device on the bus.


The 2nd number (to the right of the dash) counts the various failed communications,

this can be due to:

  • CAT5 cable not crimped properly
  • Collision of addresses(devices having the same address)
  • Noise or Interference from other electricity.


                        Picture of an Unstable Bus:



To Solve an Unstable Bus

  • Double check and triple check your CAT5 Crimp (especially if this is new system being installed)
  • Check to make sure all your CAT5 crimps are properly inserted into the CAT5 ports on the devices (Disconnect and reconnect the cat5 cables to their ports)
  • Resetting the Main Light Control Panel or the Master Control Panel.
  • Where you have Dropped Off devices, those devices might have failed, check to see if they appear to be powered up, Reset them to see if they are still operational.
  • If they operate intermittently, then try to bypass them with a CAT5 Coupler to see how the system behaves without that device.


  • If the problem still persists call Tech Support.


The problem is no longer present when the errors are not compiling and all your devices are present on the Bus Scan Display.


Most Common Solutions to Unstable Bus:

  • Finding a Bad Cat5 Crimp
  • Resetting the master and reconnecting the Cat5 cables.
  • Finding a device that failed and replacing it on with a functioning device (can be panel or switch).


Was this article helpful?
0 out of 0 found this helpful
Have more questions? Submit a request