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electronics for automotive use. It is slightly faster than the bean bus and has more data per command, but is still much slower than CAN, since realtime speeds are not required AVC-LAN TOPOLOGY TRANSMISSION Topology in the recent Toyota Corolla, Prius, Sienna, and Lexus models have been shown to have a star topology. All audio and video components are connected to a central head unit that manages all control signals. This tends to be either an AVC-lan compatible receiver and/or a multi-display. as previously stated the AVC-LAN is a derivation of the IEBus. The AVC-LAN operates at 17. 8 kbps with 0-32 Bytes of data in each command, making it compatible with IEBus mode 2 Data on the avc-Lan (iEBus mode 2)travels over shielded twisted pair wire. The bus vollage levels range from-05V to 6.0V. voltage differential is used to represent a logic l or zero. A voltage difference of 20mV or less represents a logic l, and a voltage difference of 120mV or more represents a logic 0. Bus ends are terminated with 120 ohm resistors and individual devices(ecus)on the bus are protected by 180 ohm series protection resistors For the ieBus synchronization is established for each bit. Transmission of each bit consists of a preparation period, a synchronization period and a data period Synchronization and data periods are lmost equal in duration. Preparation consists of a period at logic l. Following that is a logic 0 period Tor synchronization Finally is a period that is either low or high to indicate the bil value Figure 1 shows the series of logical states that make up each transmitted bit(twice). This can be compared to figure 2 to see what each bit looks like when actually transmitted over the AVC-laN figure 1: Logical Transmission of AVC-lan bit Logic 0 Preparation Synchronization Data period Preparation Synchronization Data period d period period ogic 1: The potential difference between the bus lines (the BUS+ and BUS-pins) is 20 mv or less (low levely Logic O: The potential difference between the bus lines( the bUs+ and BUs-pins) is 120 mv or more(high level figure 2: AVC-LAN Signal(Header, Master, slave field of MfD calling JBL for beep start bit bit 0 bit 1 ACK IX+TX- omv/div 型4915-800mv/div TX-B5-7 500 mv/div Looking at scope captures of figure 2 (where each division is 100 microseconds) the preparation period takes about 7 micro-seconds synchronization takes about 20 and the bit data takes about 13 microseconds. The start of a transmission is indicated by an extended high level state for the start bi When transmissions are completed the voltage difference drops and maintains a low level A specific connector doesn't seem to be required, since Toyota uses multiple connector types on its audio bus. A six pin Molex connector is common for the IEBus. This connector contains pins for 12V Ignition, Ground, TX+, and TX- which correspond to pins 1-5(respectively) in figure 2. Audio equipment for Toyota typically uses a 12 pin R4 connector. This is the typical connector for CD changers, receivers, and amps. As opposed to the typical iEBus connector, the r4 connector contains addilional lines for an eject signal, mute, speaker ground, and stereo speaker lines consisting ofR+, R- L+,and L As we can see the Toyota avc-lan R4 connector provides for a stereo analog audio line to be included in the same harness as the control lines. Notice there is no auxiliary inputs or outputs for any device. Rather Toyota uses serial data transmitted over the bus to control which device is supposed to be using the stereo lines at any given time. Multiple devices may exist on the bus and all may be capable of injecting audio onto the stereo lines but the head unit will dictate who is supposed to be controlling those lines figure 3: Typical IEBus Connector )12V 12丫3 2)Ignition 3)Power Ground 5|6 4)TX+ 5TX lEBus Molex Female figure 4: R4 Audio Connector IR-2)L+ 3)S-GND 54 321 4MUTE 5)12V 6)R-7)L-8)GND 121109 8 76 9)T-10Tx+ I rEject 12)Ignition R4 Connector Toyota also uses other connectors on the avc-lan, specifically where video or microphone signals are required. Many models with integrated navigation, back-up cameras, hands-free telephones, or DVD-players use N2, N3, and N4 connectors to transport video and microphone signals in addition to the signals that run through the r4 connectors on the avC-Lan. Figure 5 shows these connectors on a 2004 Prius Navigation ECU. The same basic configuration is shared on Sienna, Lexus, and other models with navigation options. Sienna and lexus schematics indicate these same connectors are utilized to integrate entertainment systems Video for models prior to 2006 seem to be supported through separate analog red, Green, Blue, and Composite Synchronization signals (rGBs)passing through the N3 connectors. Images are NTSC interlaced with horizontal sync at about 15 75kHz having 30 complete image frames a second(60 interlaced). Resolution on 2004-2005 models is reported to be 800 by 480(while others say it's 400 by 234). As an interesting side note some individuals have been able to inject Vga signals through the n3 by using powerStrip or SwitchResX for Windows and Mac os X respectively and a homemade cable harness. Often additional hardware is required, since many graphics cards don 't support composite sync or interlaced modes and these options are rarely advertised even when they do. Some 2006 models are known to transmit video digitally, although the speci fics of this are currently vague at be figure 5: Connectors N2 ,n3,n4 on 2004 Prius navigation ECU DL口u 密昌 004PR# 9 v P002 4pJen papule to90-o 门验的体 elLey'oy-BMmo4;0600分-Lt898 7dH:024P明d103日 pnpa sy LOAOJ RQ=H重956的TPR1,ACFD对AOp WITE SYNC ALWAYS ACTIVE AND RGB ACTIVE FOR MAP, DEST, MENU ONLY ACHP工时HAs0,10 IE INPUT C TO GND AUDIO OUT COAX IAL ANTENNA CONNECTOR 13.5 D COMMUNICATION PROTOCOL: Every command over the iEBus follows a particular format consisting of a Header, Master Address Field, Slave Address Field, Control Field, Data Length Field, and Data Field(s). Communication is either from one device to another or is broadcast to all devices on the bus each device on the bus has a unique identifier(address) that says what kind of device it is. Only one device may exist per address so multiple devices of the same type may not exist unless there is a secondary identifier they are capable of assuming figure 6: Basic IEBus Communication Frame/Packet aster Slay Header Cortrol Field Length lta field Field Field Field 121 141181181181 Start aster Slave Control Addres/p PAB Data Ei Ca PA LengthE bits P A Eit PA Bits The Header consists of the start bit and a broadcast bit. The start bit has an extra long high signal that denotes the start of communication and is always considered a 1(see figure 2). Immediately following this is the broadcast bit This bit is a i to denote direct communication to another device oro to denote a message broadcast to all devices The Master Address field is composed of 12 biLs telling what device is sending the message and 1 parity bit. Even parity is used here and for all other parity checks. Therefore, when the number of 1's in the master address bits is odd the parity bit should be set to 1. This will make the number of 1's in each field (including the parity bit)always even. If this is not the case a transmission error occurred and the receiving slave device should not acknowledge the transmission The Slave Address field is also 12 bits with a parity bit. An additional bit follows, with value 0, that provides time for the slave device to further increase the voltage differential on the twisted pair and indicate that it acknowledges the receipt of a valid message to it. Values for the 12 bit addresses come from a shared list of device type identifiers that are common across Toyola automobiles. For general broadcast the slave address is set to FFF(hex). Some of the more common and known address numbers are(in hex) 110-Multi Function Display(MFD) 120-AyX 128- IDIN TV 140-AVN 144-G-Book 160- Audio h/u 178-Navigation 17C-MONET 190- Audio h/u 1AC -Camera-C 180- Rr-TV 1C0-Rr-CONT 1- TV Tuner 2 1 C4- Panel 1C6-G/W I C8- FM-M-LCD ID8-CONT-SW IEC-Body 1F0- Radio tuner 1F1-XM Radio 1F2- sirius 230-TV-Tuner 240-CD-CH2 250- DVD-CH 280-Camera 360-CD-CH1 3A0- Mini-Disk Ch 17D- Telephone 440-DSP-Amp 530-EtC 5C8- MAYDAY 1A0-DVD-Player ID6-Clock 1F4- RSA 1F6- RSE 480-Amplifier As some additional clarification, 190 seems to be the h u on the prius and 1 60 on the corolla Commands for controlling bass, treble, fade, and balance are completely different between these vehicles. This may be related to the prius data pertained to a system with a JBL amp. With this system 440 was addressed by 190, rather than a broadcast from 160, to control these values also when navigation and MFD systems are present, touchscreen events may be sent from 110 to 178 Four control bits, a parity bit, and an acknowledge(ack)bit make up the control field. Control field values themselves vary depending on the receiving device. Documentation of these values are not in Toyota manuals available to the public. There are groups of home-brew hardware developers that have compiled some values for AvC-lan control fields for a few types of hardware. This requires having a piece of equipment of that type and being able to capture and analyze messages to and from that equipment. Needless to say these lists are very limited and incomplete The data length field tells how many data fields to expect. These values are dependent upon the control field and slave address, so knowledge about them is also very limited Data length has 8 bits followed by a parity and acknowledge bit. values of ohl to ohf define l to 15 trailing data fields and oho denotes 16 trailing data fields. Data fields also consist of 8 bits with parity and acknowledge bits. The data fields are used to contain information that describe more complex component commands Below are some common messages from the 2004-2005 Prius listed in the format <broadcast bit> master><slave> <control command> <data length><data field>(in hex excluding parity or ACK bits) Request to play beep dd=1-4 duration: <1><110><440><F><5><0 5E 29 60 dd> Press on screen(xx, yy)=(0-FF, yy=0-FF:<1><110><178><F><8><0 21 24 78 x yy xx yy> Balance bl-09 (left) to 17(right) <1><190><440><F><5><00257491bl> Fade fd=09(front) to 17(back) <1<190<440><F><5><00257492fd> Bass bs=ob (min)to 15(max) <1><190<440><F><5><00257493bs> Mid md-OB(min) to 15(max) <1<190><440><F><5><00257494md Treble tb=OB(min) to 15(max) <1><190><440><F><5><00257495tb> Volume up vu=01(min) to 04(max) <1><190<440><F><5><0025749Cvu> Volume down vd=oi(min to 04(max): <1><190><440><F><5><00 25 74 9D Vd> The number of known commands are relatively limited, since Toyota does not publish these.A standard set of commands must exist, but they are likely only available to partners of Toyota and large after-market equipment companies. The only definite way to determine if command codes will work or to find new command codes is to try known codes or monitor transmissions from units that work on the avc-lan. see the references listed at the end of this document for additional information or Sources PRACTICAL CONSIDERATIONS Since many of the parts needed to tap into and work with the avc-lan are not accessible to the general public, mechanics, or dealerships; it can be difficult for individuals to build AVC-LAN compatible circuits. The largest difficulty appears to exist for finding specialty connectors AVC LAN/IEBus driver circuits Connectors such as R4 Y-adapters are easily found at dealerships and part stores because of after- market car stereo equipment. More exotic connectors such as N2, N3, and N4 connectors can not readily be bought outside of japan even then, most individuals are currently forced to buy complete (and expensive) harnesses and cut off the ends to make adapter cables. dealerships will not usually be able to order video avc-lan connectors, even though they plainly are listed in the repair manua Places like japanparts com may be the only result in such instances Commercial chips do exist from neC that handle most issues of communication on the IeBus Unfortunately these chips must be purchased in very large quantities and can only listen to broadcasts or messages directed specilically at them. These chips are targeted at operating as a simple stand-alone slave device, which makes these chips useless if the construction of a AVC-LAN analyzer, message interceptor, or similarly operating device is required. Analog comparators or op-amps, when correctly biased, can convert differential signals into a 0-3.3V or 0-5v digital signal that is more useful with typical digital electronics. Some proven designs use the LM339 in this capacity. The resulting signal is then typically sampled at intervals shorter than 7 microseconds by a micro-controller or other digital logic mechanism, so that major transition states are captured (although 3.3 microseconds aka 300kHz or less would be safer) Possibly as time goes on and more products support Avc-lan the technologies that support it wil become more common and available to the common man at that time a cost may also become reduced to build interfaces to the avC- lan or competitively priced and more complete and developed solutions will be available CONCLUSIONS While all the mysteries of the Toyota automobile audio bus have not been revealed, enough has been uncovered here to understand and work on basic devices. The avc-lan is based upon the more strict and better known standards of the IEBus. This specifies reasonably well known methods for signal transmission, definition of logic bits, and message structure in regards to headers and transmitted data Specifics of the AVC-lan are related more to standard addresses of particular types of equipment that may exist on the bus, control commands, and data fields used to manage devices on the bus Being a proprietary format toyota can and does add ways for new components to interact on this bus without notice. Still, basic functionality must be maintained to support after-market add-ons and allow reuse of components across multiple models. Identification of standard device types on the network was made, as well as some of the messages that are passed between them. This information should stay the same for common components that will have long lifetimes or go through multiple revisions. The serial interface of the bus system is flexible enough to allow new features to be added while maintaining previous features device into the audio or entertainment system of a modern Toyota could be further explored and ble Overall enough layers of this system have been adequately revealed here that integration of a sim accomplished. From physical interface to electronic signaling and messaging protocols, the control mechanism can be reasonably understood and worked with. The avc-lan is less of a mystery and more of a tool that can be used and mastered Works cited Davis, Leroy. Inter Equipment Bus: IEbus Description. " Interfacebus com 2 July 2006> LSI Device for Inter Equipment bus (iebus) Protocol Control. MOS Integrated Circuit uPD72042B Data Sheet. s13990EJ3VODS00 (3rd edition). NEC, August 2002 Norm(flier). Designer of Hybrid Interfaces CA'S CAN-view Personal Interview. 15 June 2006 Slonicki Marcin " AVC-Lan-how it work? Toyota Corolla MP3 Player project. 2006 chttp://www.softservice.compl/corolla/avc/avclan.php> Audioandelectronics"priusChatJune2006.<http:/> Body Electrical- Multi Display 2004 Prius Misc Feature Manuals. Toyota Motor Corporation, 2003.BE35,BE53-BE54. Body Electrical- Multiplex Communication. 2004 Prius Misc Feature Manuals. Toyota Motor Corporation, 2003. BE4-BEl0 Electrical Wire Routing-G. 2004 Prius Electrical Wiring Diagram. Toyota Motor Corporation, 2003.48-49 ystem Circuits-H: Multiplex Communication System-AVC-LAN Bus. 2004 Prius Electrical Wiring Diagram. Toyota Molor Corporation, 2003. 78-81 abasic description top -level interconnect drawings of AVC-LAN System Circuits-H: Multi-Display and Audio system with Seperate amplifier. 2004 Prius Electrical Wiring Diagram. Toyota Motor Corporation, 2003. 326-335 *detailed AvC-lan circuits with connector references to"Electrical Wire routing System Circuits-H: Multi-Display and Audio System with Built-in Amplifier 2004 Prius Electrical Wiring Diagram. Toyota Motor Corporation, 2003. 336-341 *detailed AVC- lan circuits with connector references to "Electrical Wire routing Connector List-K. 2004 Prius Electrical Wiring Diagram. Toyola Molor Corporation, 2003. 391 392. *contains drawings of connectors pin numbering Part Number of Connectors -L. 2004 Prius Electrical Wiring Diagram. Toyota Motor Corporation, 2003.391-392 references Toyota connector labels to part number Overall Electrical Wiring Diagram -M: Multi-Display and Audio System with Seperate Amplifier 2004 Prius Electrical Wiring Diagram. Toyota Motor Corporation, 2003. pp394-396; chpt2, 4, 19-20 Drawings showing all circuits together- long more difficult to follow

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