Spiegazione I-Bus da OpenBMW.org

Da [Devi essere iscritto e connesso per vedere questo link]




I-Bus Protocol
CREDITS: The I-Bus was originally reverse-engineered by Thomas
L. Wood for the MPorty/Cajun
MP3 Project. [Devi essere iscritto e connesso per vedere questo link] was
his original write-up of it. Richard
Naninck performed additional research and wrote the first general-purpose
I-Bus message decoder for intercepting Video Module messages. Ed
Anuff identified the I-Bus as being based on the ISO 9141/K-Bus
protocol and documented the semiconductor manufacturers who supply
devices supporting it.
Since then, a Yahoo! Group has formed to discuss the technical details
of the I-Bus, appropriately named [Devi essere iscritto e connesso per vedere questo link].
Along with the OpenBMW
Yahoo! Group, this represents a valuable forum for discussing
issues related to I-Bus interfacing and members of both groups regularly
post useful information.
IMPORTANT: This information is provided for reference purposes
only. Use this information at your own risk.
BMW's I-Bus is based on ISO 9141 and K-Bus (The protocols used by
OBD-II). It is basically a second K-Bus in the car for handling interfacing
between the radio, CD, navigation, and telephone systems. In particular,
the steering wheel controls for the radio, CD, and phone utilize
the I-Bus.
The I-Bus is a single wire bus that is a white/red/yellow wire which
is available at a number of different connectors inside the car such
as at the CD changer connector in the rear, the phone connector in
the center console, etc.
The bus' physical layer is an open collector setup pulled high (+12v)
by the bus, and pulled low by the talker. This means that the idle
voltage on the wire is +12v (the battery voltage, or Vbatt). This
is somewhat similar to RS232 signalling, and like RS232, an interface
IC is needed to turn this into a TTL digital signal that can be understood
by a microcontroller. Later in this document, several off-the-shelf
parts will be listed that can be used to easily drive this sort of
signal.
Serial communications on the bus are 9600 bps, 8 data bits, Even
parity, 1 stop bit.
An I-Bus packet contains the following bytes of data:

Source Address

Length

Destination Address

Data Bytes

XOR Checksum

Unlike most similar single wire network protocols, the I-Bus has
no apparent way to identify the start of a packet, so this must accomplished
in software by looking for a delay between messages.
The following device addresses have been decoded for the E39 5-series:

0x00	Broadcast
0x18	CDC CD-Player
0x3B	NAV Navigation/Videomodule
0x43	MenuScreen
0x50	MFL Multi Functional Steering Wheel Buttons
0x60	PDC Park Distance Control
0x68	RAD Radio
0x6A	DSP Digital Sound Processor
0x80	IKE Instrument Control Electronics
0xBF	LCM Light Control Module
0xC0	MID Multi-Information Display Buttons
0xC8	TEL Telephone
0xD0	Navigation Location
0xE7	OBC TextBar
0xED	Lights, Wipers, Seat Memory
0xF0	BMB Board Monitor Buttons
0xFF	Broadcast

A packet containing the following bytes would display "CD 7-04" on
the Radio MID Display:
68 17 ff 23 c0 30 07 20 20 20 20 20 08 43 44 20 37 2d 30 34 20 20 20 20 45
S L D Data 'C''D'' ''7''-''0''4' C
r e s h
c n t k

A full set of button codes is available [Devi essere iscritto e connesso per vedere questo link].
Below is an example of a track title displayed on an E39 MID Radio
Display from an in-car MP3 player (Courtesy of Thomas
L. Wood):
Interfacing
Typical projects as well as general experimentation call for some
form of I-Bus to RS232 interface so that I-Bus packets can be captured
and displayed on a laptop or other device in order to be decoded.
Because the I-Bus uses the physical layer of the ISO9141/K-Bus, it
is fairly easy to build a connector from off-the-shelf IC parts or
to even potentially take an existing OBD-2/RS232 adapter and connect
the K-Line from it to the I-Bus.
If building an adapter from scratch, utilizing an off-the-shelf
K-Bus interface/transceivers should save a lot of effort. The advantage
of a design using a K-Bus interface chip of some sort is that most
of these chips deal with a number of issues such as bus contention
and not overloading the bus that make them a safer choice. There
are a number of good choices for this, which are listed with links
to their manufacturers below. Another option is to attempt to use
a tranceiver that is compatible with the LIN
(Local Interconnect Network), which is also based on ISO9141
but runs at a faster speed. Any of the listed interface/transceivers
should couple very nicely with a Maxim MAX232, which handles can
drive standard RS232 communications to a laptop or small embeddable
computer such as the Advantech
PCM-5820. While it is possible to interface to the I-Bus without
a K-Bus tranceiver IC, BMW's own products, like the Video Module,
use K-Bus chips from companies such as [Devi essere iscritto e connesso per vedere questo link]. [Devi essere iscritto e connesso per vedere questo link] is
a popular choice for obtaining these types of interfaces since they
have a web store that sells single unit quantities. Many hobbyists,
however, prefer to use interfaces built using transistor circuits
and have had success in doing so.
Depending on the application, for example building an adaptor to
control a hands-free phone kit, connecting to a full PC would not
make sense and instead some sort of low-cost microcontroller would
be used. The CD-Changer adapters from companies like [Devi essere iscritto e connesso per vedere questo link] and
others are examples of this. Hopefully, this information will spur
hobbyists to create an assortment of interface kits for controlling
a number of different in-car electronics.


Useful Parts For Building Adapters
K-Bus/I-Bus Interface/Transceivers
Melexis
TH8080 LIN/K-Bus Transceiver [Devi essere iscritto e connesso per vedere questo link]
Melexis
TH3122 K-Bus Transceiver with integrated Voltage Regulator [Devi essere iscritto e connesso per vedere questo link]
ELMOS
K-Bus transceiver [Devi essere iscritto e connesso per vedere questo link] target="_blank" rel="nofollow">Motorola
MC33290 K-Line Serial Link Interface [Devi essere iscritto e connesso per vedere questo link] target="_blank" rel="nofollow"> target="_blank" rel="nofollow">Motorola
MC33199 Automotive ISO 9141 Serial Link Driver [Devi essere iscritto e connesso per vedere questo link] target="_blank" rel="nofollow">
Atmel U6812B Single-Ended Bus Transceiver [Devi essere iscritto e connesso per vedere questo link]
ON Semi NCV7310 Single Wire LIN Transceiver [Devi essere iscritto e connesso per vedere questo link]
Philips
TJA1020 LIN transceiver [Devi essere iscritto e connesso per vedere questo link]
Infineon TLE 6258 Single-Wire-Transceiver [Devi essere iscritto e connesso per vedere questo link]
RS-232 Driver/Receivers
Maxim
MAX232A +5V Powered, Multichannel RS-232 Driver/Receiver [Devi essere iscritto e connesso per vedere questo link]