AN1816 datasheet(2/24 Pages) FREESCALE

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AN1816

Application Note

Distributed Systems Interface (DSI) Overview

The Distributed Systems Interface (DSI) was designed to interconnect

multiple remote sensor and actuator devices to a central control module.

It provides simultaneous support for sensors and actuators using a

2-wire bus that provides both power and communications. This results in

savings in wiring costs and connector complexity. Unlike conventional

systems, the size of the connector for the control module does not need

to grow to accommodate every new sensor or actuator. A new sensor or

actuator can be added to the bus without reconfiguring the system

design. The DSI, therefore, enables the development of easily

expandible systems.

The DSI communication bus is simple yet robust. Signals are

superimposed onto the power line and, as communication between the

master and slave nodes is bi-directional, the DSI makes efficient use of

bus bandwidth. Also, to ensure message integrity, each message

contains a 4-bit Cyclic Redundancy Check (CRC).

Slave nodes can be attached to the bus in daisy chain or parallel

connections. Each slave device on a bus has a unique address. The

daisy chain connection allows the central module to establish the node

addresses at power-up. The parallel configuration can be used for

devices that have pre-programmed or fixed addresses. It is possible to

have a combination of the two on one bus with the maximum number of

nodes on a DSI bus being 16 (1 master and 15 slaves).

Signalling

The DSI uses two mediums for signalling - voltage mode for messages

from the master to the slaves, and current mode for the responses from

the slaves.

Voltage Mode

Encoding

The voltage mode signal bits are sent on a 2:1 ratio as shown in Figure

1 Voltage Mode Bit Encoding.

Figure 1 Voltage Mode Bit Encoding

Logic 1

Logic 0

Logic 1

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AN1816 Datasheet(PDF) 2 Page - Freescale Semiconductor, Inc