Controller Area Network (CAN) is a serial communication protocol developed primarily for applications in the automotive industry. It is also capable of offering good performance in other time-critical industrial applications.
The CAN protocol is optimized for short messages and uses a carrier sense multiple access (CSMA)/Arbitration message priority (AMP) medium access control technique. Therefore CAN protocol is message oriented, and each message has a specific priority that is used to arbitrate access to the bus in instances of simultaneous transmission.
Related: Basic Features of Foundation Fieldbus (FF)
The bit stream of a transmission is synchronized on the start bit, and the arbitration is performed on the following message identifier, in which a logic zero is dominant over a logic one. A node that wants to transmit a message waits until the bus is free and then starts to send the identifier of its message bit by bit. Conflicts of access to the bus are solved during the transmission by an arbitration process at the bit level of the arbitration field, which is the initial part of each frame. Therefore, if two devices want to send messages at the same time, they first continue to send the message frames and then listen to the network. If one of them receives a bit different from the one it sends out, it loses the right to continue to send its message, and the other wins the arbitration. With this message method, an ongoing transmission is never corrupted, and collisions are non-destructive.
A typical example of technology that is based on CAN specification is the DeviceNet which has received considerable acceptance in the manufacturing applications at the device level. The DeviceNet specification is based on the standard CAN protocol with an additional application and physical layer specification.
The DeviceNet frame has a total overhead of 47 bits which include: start of frame, arbitration (11-bit identifier), control, cyclic redundancy check (CRC), acknowledgement packet (ACK), end of frame, and intermission fields. The size of a data field is between 0 and 8 bytes. The DeviceNet protocol employs the arbitration field to provide source and destination addressing as well as message prioritization.
Recommended: The Ultimate Guide to Electrical Maintenance
Related: Features of HART Communication Protocol
The major shortcoming of CAN network compared with other networks is the slow data rate, limited by the network length. Because of the bit synchronization, the same data must appear at both ends of the network simultaneously.
DeviceNet which is based on CAN network specification has a maximum data rate of 500 kbps for a network of 100 m. Therefore the throughput is limited compared with other control networks.
CAN network is also not suitable for the transmission of message of large data sizes, though it does support fragmentation of data that is more than 8 bytes into multiple messages.
You can also read: How RS-232, RS-422 and RS-485 Networks are applied in Instrumentation
The importance of printed circuit board (PCB) technology has escalated throughout the years with the…
One of the key challenges in measuring the electrical current in high voltage, high power…
The Concept behind Wiegand Effect Based Sensors The Wiegand effect technology employs the unique…
An accelerometer is a sensor that is designed to measure acceleration or rate of change…
The USB-6009 is a small external data acquisition and control device manufactured by National Instruments…
X-Y tables are utilized as components in many systems where reprogrammable position control is desired.…
View Comments