Encoder MEM40B –MEM41B with CANopen protocol –Instruction Manual
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MEM40B_CAN_Inglese_ul.docx
Absolute Encoder with CANopen protocol, Class C2
1. CAN bus & CANopen protocol
1.1 CAN bus
The CAN bus (CAN: Controller Area Network) was originally developed by Bosch and Intel as a means of
fast, low-cost data transmission in automotive applications. The CAN bus is used today also in industrial
automation applications.
The CAN bus is a field bus (the standards are defined by CiA, the CAN in Automation Association)
through which devices, actuators and sensors from different manufacturers can communicate with each
other.
Elap encoder complies with standards CiA DS 301 “Application Layer and Communication Profile” and DS
406 “Device Profile for Encoders.”
1.2 CAN bus Characteristics
Data rate of 1 MBaud with network expansion up to 40
Network connected on both sides
The bus medium is a twisted-pair cable
„Real-Time‟ operation: a max wait time is set for high priority messages
Theoretically 127 users at one bus, but physically only 32 are possible (due to the driver).
Ensures data consistency across the network. Damaged messages are notified as faulty for all
network nodes
Message-oriented communication: the message is identified by a message identifier. All network
nodes use the identifier to test whether the message is of relevance for them.
Broadcasting, multicasting: All network nodes receive each message simultaneously. Synchronization
is therefore possible.
Multimaster capability: Each user in the field bus is able to independently transmit and receive data
without being dependent upon the priority of the master. Each user is able to start its message when
the bus is not occupied. When messages are sent simultaneously, the user with the highest priority
prevails.
Prioritization of messages: The identifier defines the priority of the message. This ensures that
important messages are transmitted quickly via the bus
Residual error probability: Safety procedures in the network reduce the probability of an undiscovered
faulty data transmission to below 10 -11. In practical terms, it is possible to ensure a 100% reliable
transmission.
Function monitoring: Localization of faulty or failed stations. The CAN protocol encompasses a
network node monitoring function. The function of network nodes which are faulty is restricted, or they
are completely uncoupled from the network.
Data transmission with short error recovery time: By using several error detection mechanisms,
falsified messages are detected to a high degree of probability. If an error is detected, the message
transmission is automatically repeated.
In the CAN Bus, several network users are connected by means of a bus cable. Each network user is
able to transmit and receive messages. The data between network users is serially transmitted.
Examples of network users for CAN bus devices are:
Automation devices such as PLCs
PCs
Input and output modules
Drive control systems
Analysis devices, such as a CAN monitor
Control and input devices as Human Machine Interfaces (HMI)
Sensors and actuators
1.3 CANopen
Under the technical management of the Steinbeis Transfer Centre for Automation, the CANopen profile
was developed on the basis of the Layer 7 specification CAL (CAN Application Layer). In comparison with
CAL, CANopen only contains the functions suitable for this application. CANopen thus represents only a
partial function of CAL optimized for the application in hand, so permitting a simplified system structure
and the use of simplified devices. CANopen is optimized for fast data exchange in real time systems.
The organization CAN in Automation (CiA) is responsible for the applicable standards of the relevant
profiles.
