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BUSnet provides a cost-effective and robust communication network for
switches, sensors and actuator applications.
BUSnet is an open standard, no royalties, licensing fees or costs for
intellectual property. Creative Commons and/or GNU licenses will apply.
Some of the main features are...
Level 1 (physical)
- Wide supply voltage, VBAT can range between 7 and 30 volts.
- Currently uses RS-485 transceivers but other PHYs
can be used or even mixed.
- Redundant-ring or line wiring topology.
- Bit rates from 300 to 115200 with bit rate detection.
- Bit rates can vary, different rates allowed on different links.
- Nodes can be neatly daisy-chained.
- Up to 1.2k (4000') between each node.
Level 2 (transport)
- Implements a "publishing and subscribing" (AKA broadcast)
model, nodes publish at will and subscribers act on the published
data.
- Unicast frames addressed directly to a node are also supported.
- Multi-master, nodes can transmit at will.
- High level of error detection (relative to the
intended applications) for reliability, including frame-length field
and CRC.
- Can be used as is or as a transport mechanism for a higher-level
protocol.
- Plug-n-play, automatic allocation of addresses, no DIP switches.
- Normal user frames with payloads up to 32 bytes.
- Fragmented user frames up to 4096 bytes.
- System-wide timestamp with 1mS resolution.
- 255 physical nodes each with an unlimited number of IO points.
- Spatial reuse, multiple frames can be travelling simultaneously.
- Intelligent frame routing to reduce traffic and latency.
Level 3 (application)
Note that Level 3 will be based on the old BUSnet
protocol which was master/slave and will therefore have to be substantially
modified. The points below are essentially a wish list at present.
- High level of safety with “interlocks”,
“feedbacks”, “timeouts”, security levels.
- Scaling and non-linear transforms can be applied
to sensor readings.
- Event logging with 1mS resolution.
- Points can read/display metric or imperial values.
- Points report in engineering units.
- Expandable, start with an single sensor node and
a display node, then add features over time.
BUSnet is designed to be easy to develop for and easy to install, some
of the design concepts are.
- Standard wiring –
BUSnet uses any 6-core cable. RJ12 modular jacks and telecom cables
are preferred but anything can be used.
- Standard async data
– BUSnet uses standard asynchronous 8N1 serial protocol
on the network.
- Easy development
– Because BUSnet uses standard async communications diagnostic
equipment is kept to a minimum and really amounts to a simple logic
analyser, oscilloscope, or serial analyser.
There are other networks around of course, but they have either too
many features or too few. BUSnet is the following...
- Open – Some of the
existing networks are closed; you have to buy everything from the
network vendor. Others are “open” but you have to pay
$1000s to join the consortium or buy the spec. That’s not open
to a hobbyist or even a small business. All BUSnet code and designs
are available free of charge under Creative Commons or GNU licenses.
- Simple – The BUSnet
hardware is trivial, any electronics enthusiast can design for the
network. The application-level software is also very simple and effectively
amounts to interfacing with an I2C port.
- Robust – Many simple
networks have little or no protection from ESD, short circuits, open
circuits etc. Some even connect processor MosFET inputs directly to
the outside world. BUSnet uses RS-485 line drivers, a genuine industry
standard that provides a very high level of protection and fault tolerance
to the low-level hardware, high ESD protection and low EME. BUSnet
also has safety features built into the protocol.
- Small – Some existing
networks require a huge amount of hardware even for a small node.
I’ve seen one that needs about 9 square inches of PCB for the
simplest node, while another needs 28 components. With BUSnet it is
possible to build a functional (albeit very simple) node on a PCB
about 12mm (½”) square using three active and three passive
components.
- Informal – Many networks
require a system to be “designed” and “tuned”
then “implemented”. Make changes and the process has to
be repeated and in some cases processors even have to be re-flashed.
BUSnet is very informal, you can start with a couple of nodes then
add nodes as and when requirements or finances dictate. When the time
comes just buy or build another node and plug it into the system.
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