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The Distributed Systems Interface (DSI) is a versatile and powerful bus protocol designed to interconnect multiple remote sensor and actuator devices to a central control module. The principal target application for the network is automotive airbag systems. Some of the characteristics for this application are the need for a low cost, highly robust, moderate speed interconnection limited to two wires. In addition it must failsafe, be deterministic, and have good EMC characteristics. Even though devices with all levels of intelligence and programmability may connect to the network, remote devices must be realizable with simple state machines. Since module size is very important a minimum of components in both the central module and remote units is critical.

Airbag systems have many types of components that may be connected to the network. Typically, these components are delivered from suppliers directly to the vehicle assembly plant. Some may be embedded in instrument panels and steering columns, others in seats, potentially others in the wiring harness. The number of remote devices is typically in double digits. For these reasons it is highly desirable to allow network addressing to be self configuring at power-up. This minimizes the number of device types, and eliminates the need for special programming equipment at component suppliers and the vehicle assembly plant.

The above issues were paramount in the development of the DSI. To maintain determinism without sacrificing bus bandwidth and simplicity a single master /multiple slave configuration is used. Robustness is maintained through the use of message cyclic redundancy codes (CRC) and remote self diagnostics. High message density at moderate speeds and cost are facilitated by the simultaneous transmission of power, master commands, and slave responses. In a single ended configuration, one of the wires can be ground. An optional daisy chain interconnection method is defined which allows the assignment of network addresses at power-up with a priori device information stored in the central module.

There are two variations on this Bus Standard, Standard and Enhanced. Standard and Enhanced devices can be mixed on a bus and use Standard DSI operation. Enhanced DSI bus operation requires that all devices on the bus be compatible with the Enhanced DSI standard.