ppt devicenet
TRANSCRIPT
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??