SAE J2366-1L-2001 ITS Data Bus.Low Impedance Stereo Audio (LISA).pdf

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SURFACE VEHICLE 400 Commonwealth Drive, Warrendale, PA 15096-0001 RECOMMENDED PRACTICE J2366-1L ISSUED NOV2001 Issued2001-11 ITS Data BusLow Impedance Stereo Audio (LISA) TABLE OF CONTENTS 1.Scope. 2 2.References. 2 2.1Applicable Publications 2 2.1.1SAE Publications 2 2.2Related Publications. 2 2.2.1SAE Publications 2 3.Definitions.2 3.1Audio Arbitration.2 3.2IDB-C2 3.3ITS 2 3.4LISA 2 3.5Receiver . 2 3.6Transmitter . 2 4.The LISA Bus . 3 4.1Transmitter . 3 4.1.1Number of Transmitters 3 4.1.2Transmitter Output . 3 4.2Receiver . 4 4.3Bus Load Resistor4 4.4LISA Connections. 4 Appendix A LISA Circuit Examples5 A.1.1Transmitter Circuit 5 A.1.2Receiver Circuit 6 A.1.3Transceiver Circuit7 A.1.4Grounding Example 8 Figure A1Example Transmitter Circuit. 5 Figure A2Example Receiver Circuit. 6 Figure A3Example Transceiver Circuit. 7 Figure A4System Grounding Example. 8 SAE J2366-1L Issued NOV2001 -2- Table 1Transmitter Types and Usage Profiles .3 Table 2Transmitter Parameters 4 Table 3Receiver Parameters 4 1.ScopeThis SAE Recommended Practice describes the Low Impedance Stereo Audio (LISA) bus, which may be used in conjunction with the Physical Layer of the IDB-C, as described in SAE J2366-1. The audio arbitration messages used to control access to the LISA bus are specified in SAE J2366-7. The IDB-C is a non-proprietary virtual token passing bus, designed to allow disparate consumer, vehicle, and commercial electronic components to communicate and share information. 2.References 2.1Applicable PublicationsThe following publications form a part of this specification to the extent specified herein. Unless otherwise indicated, the latest issue of SAE publications shall apply. 2.1.1SAE PUBLICATIONSAvailable from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001, or http:/ www.sae.org. SAE J2366-1ITS Data BusPhysical Layer SAE J2366-7ITS Data BusApplication Message Layer 2.2Related Publications 2.2.1SAE PUBLICATIONSAvailable from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001, or http:/ www.sae.org. SAE J2355ITS Data BusArchitecture Reference Model Information Report SAE J2366-2ITS Data BusLink Layer SAE J2366-4ITS Data BusThin Transport Layer SAE J2590PMODE for In-Vehicle Networks 3.Definitions 3.1Audio ArbitrationAudio Arbitration is the process through which a Transmitter requests and is granted permission to generate audio output onto the LISA bus. When used with the IDB-C, the Audio Arbitration mechanism and required messages are defined in SAE J2366-7. 3.2IDB-CThe IDB-C is a member of the ITS Data Bus (IDB) family of networks, defined by the SAE J2366 series of documents. 3.3ITSIntelligent Transportation Systems 3.4LISALow Impedance Stereo Audio the subject of this document. 3.5ReceiverA Receiver is a device capable of accepting an analog audio input signal, e.g., audio amplifier, memo recorder. 3.6TransmitterA Transmitter is a device capable of generating an analog audio signal, e.g., CD-changer, wireless phone, text-to-speech synthesizer. SAE J2366-1L Issued NOV2001 -3- 4.The LISA BusThe LISA bus is designed to allow multiple Transmitters and Receivers to be “bussed” on a single unshielded twisted pair (UTP). One UTP is required for each LISA channel. A stereo configuration would therefore include 2 UTPs. Additional UTPs can be used for additional channels, as required. The LISA bus allows summing (mixing) of multiple Transmitters and Receivers, if desired, and is designed to be compliant with typical automotive EMC requirements. When used with IDB-C, the Audio Arbitration mechanism defined in SAE J2366-7 controls access to the LISA bus. Appendix A shows examples of a LISA Transmitter, Receiver, and Transceiver circuit, and also provides an example of an overall system grounding method that can help to reduce interference and ground potential issues. 4.1TransmitterA Transmitter always presents high impedance to the LISA bus, regardless of whether it is actually generating any audio output (Active) or not (Inactive). Transmitters fall into the categories shown in Table 1: 4.1.1NUMBER OF TRANSMITTERSThe number of Active Transmitters is limited by the Receiver input level and the type of audio transmitted by each Transmitter. It is theoretically possible to have 16 Active Transmitters providing that the Receiver input is not overloaded or the effects of clipping are not considered objectionable. The bus is specified such that it is possible to have one full volume Type 1 or Type 2 source and one full volume Type 3 source Active at the same time. Additional sources or alternate combinations can be supported by reducing the lower priority sources to low volume or muted states. It is the responsibility of the audio arbiter to manage the output level of the Transmitters such that the total signal level on the bus is within the valid range and the final audio output is not objectionable to the listener. 4.1.2TRANSMITTER OUTPUTTransmitters must operate in a high impedance state. Transmitters shall not cause audible noise or attenuation when they join the LISA bus or when powering up. Transmitters shall have single ended high impedance current drive characteristics to avoid back-loading active signals on the bus. Transmitter parameters are shown in Table 2. Transmitters may be Active (generating audio content) or Inactive (not generating audio content). The state shall be controlled by the Audio Arbitration scheme defined in SAE J2366-7. Each Transmitter shall support at least two output levels: High (full volume) and Muted. An additional Low volume output level should be supported, but may not make sense for all nodes (e.g., a backup warning aid). Additional levels may be supported at the discretion of the device manufacturer. TABLE 1TRANSMITTER TYPES AND USAGE PROFILES CategoryNameDescription Type 1PriorityThis category includes devices that would override the entertainment content for some period of time. Examples include cell phones, route guidance instructions, and driver information (voice alerts). Type 2EntertainmentThis category includes devices such as CD players, radios, talking books, and other similar devices that generate continuous audio content. Type 3Alert This category includes chimes, alerts, and other audio signals, that are very short in duration and are typically time sequenced apart. SAE J2366-1L Issued NOV2001 -4- 4.2ReceiverSince +VBatt is always present on the IDB-C harness, to minimize any audio noise, the Receiver should disable its input while powering up and when joining the LISA bus. Receiver parameters are described in Table 3. 4.3Bus Load ResistorFor current mode operation, a 600 resistor is connected across the bus pairs on each LISA channel. To remove any high frequency noise that might have been induced by outside devices, a 0.0068 µF capacitor should be inserted in parallel with the load resistor, as shown in Figure A4. A master ground point must be established to the vehicle chassis ground on the un-driven side of the 600 resistor (see Figure A4). In an IDB-C implementation, the LISA bus is typically connected to the Vehicle Services Interface (or Gateway), which connects the IDB-C to the OEM-proprietary vehicle bus, and converts the LISA audio to that required to feed the OEM entertainment radio. In this type of installation, the load resistor and filter capacitor will typically reside in the Gateway. 4.4LISA ConnectionsWhen used with the IDB-C, the Vehicle Connector defined in SAE J2366-1 can accommodate up to three LISA channels. The physical design and dimensions of the Vehicle Connector, and the LISA bus signal pin assignments are specified in SAE J2366-1. PREPARED BY THE SAE ITS DATA BUS COMMITTEE TABLE 2TRANSMITTER PARAMETERS ParameterMinimumMaximum Number of Active Transmitters0 Transmitter output impedance in Active, Inactive, or Low states500 k Transmitter signal level measured at the LISA bus connection with source at full volume 1.3 Vrms Transmitter signal level measured at the LISA bus connection with source at Low volume 0.65 Vrms Transmitter signal level measured at the LISA bus connection with source Muted 0 Vrms TABLE 3RECEIVER PARAMETERS ParameterMinimumMaximum Number of Receivers16 Receiver input impedance500 k Receiver input level2 Vrms SAE J2366-1L Issued NOV2001 -5- APPENDIX A LISA CIRCUIT EXAMPLES A.1The following circuit diagrams show how LISA Transmitters, Receivers, and Transceivers may be built. These are provided as examples only and are not guaranteed to meet all the requirements of this specification. In all circuit diagrams, it is assumed that the node will have a means for controlling the FET switches shown. The HC series 4066 FET switch available from Toshiba and others exhibits the low on resistance desired. A.1.1 Transmitter CircuitThe circuit shown in Figure A1 applies to a device that is only capable of generating audio output, e.g., a CD player, or text-to-speech synthesizer. FIGURE A1EXAMPLE TRANSMITTER CIRCUIT SAE J2366-1L Issued NOV2001 -6- A.1.2 Receiver CircuitThe circuit shown in Figure A2 applies to a device that is only capable of receiving audio inputs, e.g., an audio amplifier. FIGURE A2EXAMPLE RECEIVER CIRCUIT SAE J2366-1L Issued NOV2001 -7- A.1.3 Transceiver CircuitThe circuit shown in Figure A3 applies to a device that is capable of generating audio output and receiving audio input, e.g., a cellular phone. Notes: 1.This switch is ON for transmit and receive. It is OFF only when the transceiver is turned off to avoid pop noise at power down. FIGURE A3EXAMPLE TRANSCEIVER CIRCUIT SAE J2366-1L Issued NOV2001 -8- A.1.4 Grounding ExampleFigure A4 shows an example of a grounding scheme that may help to reduce the possibilities of noise interference, ground potential shifts, or ground loops. FIGURE A4SYSTEM GROUNDING EXAMPLE SAE J2366-1L Issued NOV2001 RationaleNot applicable. Relationship of SAE Standard to ISO StandardNot applicable. ApplicationThis SAE Recommended Practice describes the Low Impedance Stereo Audio (LISA) bus, which may be used in conjunction with the Physical Layer of the IDB-C, as described in SAE J2366-1. The audio arbitration messages used to control access to the LISA bus are specified in SAE J2366-7. The IDB-C is a non-proprietary virtual token passing bus, designed to allow disparate consumer, vehicle, and commercial electronic components to communicate and share information. Reference Section SAE J2355ITS Data BusArchitecture Reference Model Information Report SAE J2366-1ITS Data BusPhysical Layer SAE J2366-2ITS Data BusLink Layer SAE J2366-4ITS Data BusThin Transport Layer SAE J2366-7ITS Data BusApplication Message Layer SAE J2590PMODE for In-Vehicle Networks Developed by the ITS Data Bus Committee