Module Introduction
The Protocol Analyzer DSI Bus is a kind of advanced Automotive Safety Bus, which is developed by Freescale. The DSI Protocol can support the Point-to-Point, Parellel and Necklace Networks. The DSI Bus Protocol has been adopted by the manufacturers who develop the advanced Airbag System in the world, including the TRW and DENSO companies. The DSI Bus has been produced for several years. The advantage of the DSI Bus is that the distributed Slaves can be strung as a necklace, and the DSI Bus can be used to communicate and supply the Power. The Slave has a 4bits Binary Address. When the system is initialized, each Slave will be subject to an Address; it can connect 15 Slaves in total (Address “0000” is reserved).
When the MC68HC55 (Master) doesn’t communicate with the Slave, the voltage of the DSI Bus is higher than 6V, and the Master supplies the Power for all the Slaves. When the MC68HC55 (Master) communicates with the Slave, the DSI Bus transmits the Digital Signal which is 1.5V Low, 4.5V High. At that moment, the Slaves keep the normal working state according to the capacitance in the Hcap Pin. The duty cycle of the High Voltage and the Low Voltage is different for the DSI Signal in each cycle. That’s to say, when the low voltage is 2/3 cycle and high voltage is 1/3 cycle, the number is “0”; when the low voltage is 1/3 cycle and the high voltage is 2/3 cycle, the number is “1”; it also can be considered as the Non-return to Zero (NRZ) Code. The Response which is from the Slave to the DSI Command appears by way of the format of the Current Change in the DSI Bus. When the current is from small to large, it is “1”; when the current is from large to small, it is “0”. The small or large current can be switched to high or low Digital Voltage Signal by the DSI Interface Device (such as MC33790 and MC33784).

Application Field
It is mainly used in the Automotive Safety Airbag System.

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