IEBus ("Inter Equipment Bus") is a two wire bus used in the automotive industry as a communications bus between various devices (usually multimedia devices) by using half duplex asynchronous (multi-master) communication with CSMA/CD (Carrier Sense Multiple Access/Collision Detection) for access control. It allows for up to fifty units on the bus over a maximum length of 50 meters. Two differential lines are used; Data+ / Data-, often labeled as Bus(+) Bus(-).

IEBus Protocol

When I get more time I will be writing up a brief description of the step by step communications process. The short version is like this...A master talks to a slave. Each unit has a master and a slave address register. Only one device can talk on the bus at any given time. There is a pecking order for the types of communications which will take precedence over another. The IEBus in my Acura appears to run at about 50 MHz. Each communication from master to slave must be replied to by the slave going back to the master with an ACK (ackowledge) bit. If the master does not receive the ACK within a predetermined time allowance it drops the communication and returns to its standby (listen) mode.

* Mode 0
** "Uses 16 bytes/frame and runs at 3.9 kbit/s or 4.1 kbit/s."
* Mode 1
** "Uses 32 bytes/frame and runs at 17 kbit/s [6 MHz Osc.] or 18 kbit/s [6.29 MHz Osc.] "

Automotive Manufacturers Using IEBus

* Honda/Acura
** "GA-NET II"
* Toyota
** "AVC-LAN"
* Pioneer
** "IP-LAN"

IEBus Enabled IC's


The "µPD6708GT" (-a appended for the leadfree) processes the protocol of the IEBus. Because it is provided with a transmit/receive buffer, the microcontroller can concentrate on the application processing of the IEBus. Because the µPD6708 also contains an IEBus driver/receiver, it can be directly connected to the bus. [ link]

* [ PIE TOY-AUX Auxiliary Input Converter]



The "µPD72042BGT" (-a appended for the leadfree) performs all the processing required for layers 1 and 2 of the IEBus. The device incorporate large transmission and reception buffers, allowing the microcomputer to perform IEBus operations without interruption. They also contain an IEBus driver and receiver, allowing them to directly connected to the bus directly. [ link]

* [ Honda/Acura Music Link]
** [ Top HQ]
** [ Bottom HQ]



The MB90580/85 series has peripheral resources of an IE bus controller, UARTs, a 8/10-bit A/D converter, a 8-bit D/A converter, an I/O extended serial interace, a 8/16-bit PPG timer, 16-bit re-load timers, 16-bit PWC timer, a 16-bit I/O timer (a 16-bit free-run timer), a 18-bit timerbase counter/watch-dog timer, an output compare (OCU), an input capture (ICU), DTP/external interrupt circuit, Embedded peripheral resources performs data transmission with an intelligent I/O service function without the intervention of the CPU, enabling real-time control in various applications. [ link]



Renesas M16C Family

The M16C MCU Platform of products offers you a variety of choices, spanning entry-level capabilities and pricing previously associated with 8-bit MCUs; hitting many options of pin-count, RAM and ROM choices; and reaching into the high-speed processing of 32-bit MCUs — all with MCUs that are upwardly pin- and software-compatible. For communications these chip have optional clock synchronous/asynchronous shared (max 5 channels), IEBus (max 5 channels), I2C bus (max 5 channels), CAN 2.0B (max 2 channels). The only group in this family which does not have the IEBus functionality available is, the M16C/70 group. [ link]



Renesas H8S/2258 Group

The H8S/2258 Group is high-performance microcomputers made up of the internal 32-bit configuration H8S/2000 CPU as their cores, and the peripheral functions required to configure a system. On-chip peripheral functions required for system configuration include data transfer controller (DTC) bus masters, ROM and RAM memory, a16-bit timer-pulse unit (TPU), 8-bit timer (TMR), watchdog timer (WDT), serial communication interface (SCI), I2C bus interface (IIC), IEBus Controller (IEB), A/D converter, D/A converter, and I/O ports.

Supports all modes in which transfer speeds differ, from "Mode 0" to "Mode 2". Using data transmission by DTC, CPU load is reduced sharply (Approx. 1/2). Using abundant error status flags to realize appropriate error processing. [ link]

Part Numbers


External links

* [ NEC IEBus Protocol IC] - (µPD6708) This thing is hard to find for hobbyists.
* [ Basic Info] - The first result for an IEBus search on Simple and sweet.
* [ Forums] - (dead thread) Some results in recording data from the IEBus in an Acura TSX.
* [ Fujitsu MB90580] - The MB90580/85 series has peripheral resources of an IEBus controller.
* [ Marcin's Site] - This site is great for learning more about the IEBus! He has really done a great job researching this protocol as well as developing one of the first boards that can talk on the bus using an ATMEGA8. (there are active forums on his site too, [ here] .
* [ Louis Frigon (] - A great write-up with schematics and source code that interfaces with the IEBus to trick the stock head unit into enabling aux input as it would for a CD changer. It is a great learning tool for how the IEBus protocol works just by looking through the well commented firmware source code. (Adapted from work done by Marcin at [ his site] .

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