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I am designing a Fire Alarm System. Main Panel will act as Master. Manual Call Point Units will act as Slaves.Hence there will be only one Master. I want to use RS485. I am not using TCP/IP Data link. My few doubts/questions are as follows:

  1. For such a small setup can I use BACnet as my communication Protocol?
  2. If yes, I am wondering to use which data link i should be using, because every subsystem seems to be Multi Master [e.g. MS/TP].
  3. In case if it is decided to use the BACnet for my project. Which files from sources I should use. Considering minimum services required. Initially it should be a bare minimum for the sake of understanding, later i can upgrade the system. I have gone through the demo examples for PIC microcontrollers. But unable to understand it . Please help.
Israr
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2 Answers2

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  1. Yes, you can use BACnet for the communication Protocol. Over RS485 it would be BACnet MSTP.

  2. BACnet MSTP is Multi-Master, but you can have slave devices that use MAC address above 127. It gets complex when adding slave devices, lots of gotchas.

  3. I can't help you with the open-source BACnet stacks. The BACnet protocol is quite large, even to support the basics. Look into the BACnet profile for B-SS for the smallest subset of BACnet services.

Steven Smethurst
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  1. Possibly, but there is a hell of a lot to the standard (- in all honesty it could be a big investment of both time & effort). Since you've mentioned it's a Fire Alarm system (- life-safety concerns), it's tempting to consider (physical) Ethernet aka UDP/IP (or even TCP/IP) for it's theoretical speed advantage (- supposedly leaning towards being up to 1000 times faster than MS/TP), and probably less cabling faults (compared with MS/TP), although in contrast MS/TP might win-out on cable length.
  2. The nice thing about UDP/IP, is that the master-slave arrangement is not tied down by the standard, e.g. you have to implement it yourself but you have the freedom to do so as you wish; any BACnet/IP device can be a client or server.
  3. There is a few of them out there now, but as you've mentioned PIC microcontrollers, I'm guessing the C language based 'BACnet-Stack' might possibly be an appropriate choice.
DennisVM-D2i
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