MC68HC55 Datasheet, PDF (3/40 Pages) Freescale Semiconductor, Inc – Two-Channel CMOS ASIC Device

MC68HC55 Technical Data
General Description of the DSI System
1.2 General Description of the DSI System
The distributed system interface is intended as a robust serial interface
system suitable for automotive body applications including airbag safety
systems. Specific goals of this system include:
• Reduction of intermodule wiring by using a 2-conductor bus.
• Provide power to remote nodes on the same pair of wires
• Self-organizing system (modules need not be programmed prior
to installation)
• No critical timing components such as crystals in remote nodes
(subject to damage in a crash)
• Wave shaped signals to minimize electrical noise
• CRC error checking on all messages to assure message integrity
1.3 Overall DSI System Connections
The DSI system consists of:
• Master MCU such as the MC68HC16P3
• One or more DSI/D devices, one DSI/P dual analog SmartMOS
device per DSI/D
• Up to 15 remote sensor and firing units per DSI bus
In this DSI system, the master MCU will communicate with the DSI/D via
the SPI. The DSI/D will in turn communicate with a DSI/P via three wires
using CMOS levels. Finally, the analog DSI/P will interface to the 2-wire
DSI bus using a combination of pulse length encoded voltage levels for
transmission of data to remote peripheral units and current return signals
for received data at the same time. All signals on the 2-wire DSI physical
layer bus are wave-shaped to minimize electrical noise. Refer to
Figure 1-1 for the following discussion.
MC68HC55
DSI/D (Distributed System Interface – Digital)
Technical Data
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