DeviceNet and SDS

Presented by :

Ramesh Vishwanathan

Biosystems and Agl. Engineering

Goals

Introduction

DeviceNet

Smart Distributed Systems

Comparison of DeviceNet and

SDS

Introduction

An analogy –

The Functionalities provided by CAN is similar to Latin letters in human communication.

To specify a language we need a stock of words as well as grammar to build sentences.

CAN users specify their own CAN-based language, or the user decides to use a standardized CAN-based higher-layer protocol

Examples of CAN-based higher layer protocols are CANopen, DeviceNet, CANKingdom, SDC, etc.

DeviceNet

DeviceNet is an application layer protocol based on CAN 2.0A and is widely used in industrial automation

Originally developed by Rockwell / Allen-Bradley and is now an “open field” bus regulated by ODVA (Open DeviceNet Vendors Association)

It is an “open”, low level network that provides connections between simple industrial devices (such as sensors and actuators) to higher-level devices (such as PLC controllers and computers)

DeviceNet

DeviceNet

It uses a trunk line/drop line topology that

provides separate twisted pair busses for

both signal and power distribution which

significantly reduces the amount of

hardcore wiring

DeviceNet

This network allows a maximum of 64 logical nodes and supports 125, 250 and 500 Kbits/second data transfer rates

Each module is assigned some priorities/IDs, which are a function of the node number (called MAC ID) and should be unique to avoid CAN specification violation

Selectable end-to-end network distance varies with speed

125 Kbps 500 m (1,640 ft)

250 Kbps 250 m (820 ft)

500 Kbps 100 m (328 ft)

DeviceNet

Devices can be interfaced with network without removing power

Supports only Standard CAN

Uses production/consumption model for module to module transfer

Peer-to-Peer with Multi-Cast (one-to-many); Multi-Master and Master/Slave Polled or change-of-state

Components of DeviceNet Device

DeviceNet

Each of these components are organized into attributes, services (methods or procedures), and behaviors of the components

These objects are defined by DeviceNet specification. For instance, the identity object has attributes such as vendor ID, device type, and serial number.

DeviceNet

A device profile consists of

device’s object model,

I/O data format (including definition of

assembly object(s) for efficient data

transfer and,

the device’s configurable parameters

documented in electronic data sheet

(EDS)

Smart Distributed Systems (SDS)

Developed by Honeywell's MICRO SWITCH Division

is also an advanced CAN based device-level communication network bus system for intelligent sensors and actuators

The SDS Application Layer Protocol is optimized for “Smart Sensors and Actuators”, where Configuration, Diagnostic, and Process information can be embedded cost-effectively in a very small footprint

Features of SDS

Communication bit transfer rates are 125, 250, 500, and 1,000 kBaud

1500 ft maximum distance at 125 kBaud (longer with Bridge)

Maximum of 125 modules can be connected to the network

12-24VDC, 2 power wires + 2 communication wires + shield

126 logical addresses - not related to physical location on the network

Event-Driven, Master-Slave, Multicast and Peer to Peer Services

Example

Use of SDS interface with state of art sensors

Temp.

A/D

SDS

Substrate

RJ45

Press.

A/D

SDS

Substrate

RJ45

Substrate

SDS

Small and effective way to connect small devices to a master controller.

Master has 100% control of all modules.

No support for communication between modules without a master PLC.

Supports only Standard CAN.

Effective when it comes to connect I/O devices (e.g., on/off switches, proximity sensors, etc.) to a PLC, as SDS fundamentally is a point to point communication between a master (Host)

and remote I/O’s.

SDS

SDS has 2 Special APDU (Application Layer Protocol Data Unit) Forms:

Short Form APDU - Shortens the CAN message for single-bit commands such as COS, Write, and Acknowledgement. This allows for greater throughput and improved system response time.

Fragmented APDU - Allows for data messages longer than the standard 6 data byte format. Up to 256 bytes of data may be sent. This allows complex data such as ASCII strings to be sent across the network

Comparison

SDS DeviceNet

Possible bit rates 125k, 250k,

500k, 1M

125k, 250k, 500k

Protection

against modules

with incorrect bit

rate

Yes. No

Possible node

numbers.

0-125 0-63

Default node

number

125 63

Questions??