IEbus Description

IEBus [Inter Equipment Bus] is used as an In-vehicle [Automotive] support bus using half duplex asynchronous [Multi-Master] communication with CSMA/CD [Carrier Sense Multiple Access/Collision Detection] for access control. Two differential lines are used; Data+ / Data-. Two modes are defined: Mode 0 uses 16 bytes/frame and runs at 3.9kbps or 4.1kbps. Mode 1 uses 32 bytes/frame and runs at 17kbps [6MHz Osc.] or 18kbps [6.29MHz Osc.].
The IEbus allows 50 units on the bus over a maximum length of 50 meters. The IEbus is a 2-wire bus.

IEbus Electrical Interface

IEbus Cabling and Termination

The cable capacitance is rated to have 8000pF max [6MHz] or 7100pF max [6.29MHz]. It appears that load capacitors should be added between each data bus line and ground to insure that those capacitance values are meet. C_Total = 1/2 * C_Load + C_Wire. The bus is terminated to 120 ohms [+/- 5%] at each end. Series protection resistors of 180 ohms [+/- 5%] are also used. With both lines within 20mV or less a logic high is represented, when the Bus lines are different by 120mV or more a Logic 0 is produced. The bus voltage level are -0.5v to +6.0 volts.

IEbus Protocol

IEbus Transmission Signal Format

For the graph above; the length of time for all the fields in Mode 0 is 7330uS + (1590 x [ number of data fields])uS.
In Mode 1 the transmission time is 2090uS + (410 x [number of data fields])uS. P = Parity bit, A = Acknowledge bit.

Synchronization is done for every bit transmitted. The bus is idle high, taken low for the Synchronization period, then the bus enters the data period. During the data period the bus is either taken high or low depending on the data bit sent. After the data period the bus returns to the preparation period, and is idle high.
Each device on the bus has a 12 bit address. The IEBus was developed by NEC Electronics.

There are a number of similar interfaces on the Automotive Buses page, or related by purpose.

Topic Navigation: Engineering Home > Interface Buses > Cabled Interface Standards > Automotive Interfaces > IEbus Interface.

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