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µPD72042BGT Made by NEC

IEBus (Inter Equipment Bus) is a two-wire vehicle 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 and Inter Equipment Bus are NEC Electronics Corporation trademarks.[1]


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. Each communication from master to slave must be replied to by the slave going back to the master with an ACK (acknowledge) 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[edit]

  • Honda/Acura
    • GA-NET II
  • Toyota
    • AVC-LAN
  • Pioneer
    • IP-Bus

IEBus-enabled ICs[edit]

NEC's V850ES/Sx3 family devices[edit]

The V850ES/Sx3 microcontroller family is a 32-bit single-chip processor that includes the V850ES CPU core and peripheral functions such as ROM/RAM, a timer/counter, serial interfaces, an A/D converter, and a D/A converter. As for automotive LAN, the V850ES/Sx3 family is equipped with IEBus and CAN Area Network. More details can be found here


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

The µPD72042BGT as mounted on the PIE TOY-AUX


The µPD72042BGT (-a appended for the lead-free) 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



The MB90580/85 series has peripheral resources of an IE bus controller, UARTs, an 8/10-bit A/D converter, an 8-bit D/A converter, an I/O extended serial interface, an 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), an 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

  • None

Renesas M16C family[edit]

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

  • None

Renesas H8S/2258 group[edit]

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, a 16-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
  • HD64F2258TE
  • HD64F2258FA
  • HD64F2258F
  • None

Renesas V850 family[edit]

A family of 32-bit single-chip microcontrollers that include ROM/RAM, a timer/counter, serial interfaces, an A/D converter, a D/A converter. The parts listed below include an IEBus interface.

Part numbers
  • V850ES/SJ3-H
  • V850ES/SK3-H
  • V850E2/SG4-H
  • V850E2/SJ4-H
  • V850E2/SK4-H


External links[edit]

  • NEC IEBus Protocol IC - (µPD6708) This thing is hard to find for hobbyists. (Broken link, please remove)
  • Renesas V850 family
  • 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. (Broken link, please remove)