LocoNet

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LocoNet

• A network for controling
• model railroads

by Stefan Bormann (stefan.bormann_at_gmx.de)
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Contents

• LocoNet? System overview.
• Physical layer
• Packet layer
• Application layer an overview
• Loco operation
• Example FRED
• References.

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1a) System overview
Command Station
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1b) What is LocoNet?

• invented by Digitrax
• proprietory
• Peer to peer
• CSMA/CD
• 3 Layers.

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2a) Physical layer - electrical
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2b) Physikal layer - timing

• 16600 Baud, 60µs bit time
• 8N1

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3a) Packet layer

• bytes are transmitted back-to-back
• packets consist of 2, 4, 6 or N bytes
• first byte is opcode
• last byte is checksum (xor of all other bytes).

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3b) Opcode
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3c) Packet timing, net access

• CD carrier detect (defines end of packet)

• MD master delay (only master may transmit)

• PD priority delay (high prio. small PD)

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3d) Packet timing, collisions

• Collisions are avoided, by shortening the time
  between still observing the net is idle until the
  first bit is transmitted onto the net.
• Collision is detected, when a 0 is seen on the
  net, while a 1 is being transmitted
• On detection of a collision, a break (15 bit
  times 0) is transmitted.

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4. Application layer
-- an overview

• turnouts
• signals
• message exchange
• decoder programming
• fast clock
• loco operation

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5a) Loco operation

• Table with loco data in command station
• Slot Index in table Handle
• Slot is a 7 bit number
• 128 Slots
• 1..120 are loco slots
• 0 dispatch slot
• gt120 are special slots (fast clock, programming)
• loco slots have fields

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5b) Fields of a slot

• loco address (14 bits)
• state of slot (free/common/idle/IN_USE)
• protocol selection ( of speed steps, ...)
• state of loco
• speed (7 bit)
• functions (9 bits, F0, F1, ..., F8)
• consist tree
• ID (14 bits, can be a device ID of controller)

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5c) Operations on slots (requests)

• requests to master
• OPC_LOCO_ADR get slot by address
• OPC_RQ_SL_DATA get slot by slot
• OPC_WR_SL_DATA write slot by slot
• OPC_MOVE_SLOTS move slot from to
• dispatch put (destination0)
• dispatch get (source0)
• NULL move (sourcedestination!0)
• OPC_SLOT_STAT1 modify slot status

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5d) Operations on slots (responses, operation)

• responses from master
• OPC_LONG_ACK simple acknowledge
• OPC_SL_RD_DATA slot data
• realtime operation
• OPC_LOCO_SPD 7 bits of speed
• OPC_LOCO_DIRF direction and F0, ..., F4
• OPC_LOCO_SND F5, ..., F8

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6a) FRED

• FRemos Einfacher Drehregler
• Simple to use
• Can only control one engine
• speed,
• direction,
• F0, F1, F2.

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6b) FRED Example for protocol (acquire loco)
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6c) FRED Example of protocol (reconnect)
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7. References

• This clinic
• http//www.nord-com.net/ stefan.bormann/dcc/
  dcc_e.html
• Digitrax homepage
• http//www.digitrax.com
• LocoNet-Hackers mailing list
• http//groups.yahoo.com/group/loconet_hackers.