LinuxSA 16/Oct/2001
Geoffrey D. Bennett <g@netcraft.com.au>
C-Bus

Introduction
- What is C-Bus
- Using it with Linux, Documenting the undocumented
- Reverse engineering tools
- Clipsal software

What is C-Bus
- Normal electrical wiring
- C-Bus wiring, diagram

- 2 wire bus, which consists of a 4 kHz signal pulse,
  between which bit's are transmitted, biased to 32 V DC
  eg.

+32.5V        +--+           +::+            +--+
              |  |           .  .            |  |
              |  |        Data? .            |  |
 30V  ---+  +-+  +------+--+-+--+-------+  +-+  +--
         |  |           .  .            |  |
         |  |           .  .            |  |
 27.5V   +--+           +::+            +--+

         |<----------- 250 us --------->|


- Motorola HC05-B6 microprocessor, 256 byte EEPROM

- Units:
    Input:
      - Key 1, 2, 4
      - PIR
      - Light level sensor
    Output:
      - Relays (various numbers of channels (1-12?))
      - Dimmers (various numbers of channels (1-12?))
    Other:
      - Serial interface
      - Ethernet interface

- Groups
  - Connect inputs to outputs
  - Numbered from 0-255

- Examples
  Input
  - Short/Long Press/Release:
    - On/Off
    - Dimmer
    - All off/on
    - Timer
  Output
  - Logic (and/or)
    - Garage
    - Night light

Using it with Linux, Documenting the undocumented

- sersniff, customised
  - dodgy C program
  - ignore data flowing in one direction
  - customised output
- protocol
  - run Windows programming software
  - observe similarities:

    \05FF00FAFF00<CR>
    D8FF0095A9AA56996A15509926010000000000000000000000C3<CR><LF>
    D8FF5800000000000000000000000000000000000000000000D1<CR><LF>
    D6FFB000000000000000000000000000000000000000007B<CR><LF>

    \0600002101<CR>890150435F4D494E44322A<CR><LF>

    \0601002101<CR>89014B45593420202020D9<CR><LF>

  - get unit type, version
  - read eeprom
  - write eeprom
  - read ram
  - set group levels
  - listen to changes in group levels

  - Linux software
    - cbusd
    - c-bus
    - test-scroll

Reverse engineering tools:
- perl
  - pack/unpack_cbus_6_string
- cbus-sim
- sprech
  - lovely Perl program
  - connects any two either character devices or TCP streams together

Clipsal software:
- Java