CAN is stands for ControlledrArea Network. CANBUS is a communication protocol developed by BOSCH to use at automotives. When CANBUS discovered at first time, its purpose was communicating between all comlex automotive devices but now using in very wide areas. All connected devices can communicate with each other without a host computer. CANBUS needs two wires and communicates very long distances upto 1 Mbits.
Adventages of CANBUS
All control and interface units can communicate via CANBUS cable. This protocol do not use analogue signals and communicate with digital signals.
A central unit collects all datas from all devices and all devices can be managed from a central device. We can call these central devices as Brain of System.
These communication protocol is strong for the electrical disturbences. First purpose of CANBUS is using into cars and there are so many electrical systems around the data cables. So CANBUS has to be strong for these work areas.
Safe to transmit:
CANBUS based on message packets. All message packets have an special ID code. Datas will not be confused and be fetched by the target slave device. When transmitting finished the sender device also verify the datas transmission state. This is increasing the reliablity of transmission.
All devices which connected to the same CANBUS line can read the data on the line. This allows all devices to communicate each other. This is the reason of the name Controller Area Network. According to this specify of CANBUS other devices may decide something to do is good or not.
How CANBUS using in Industry?
In industry, there is always a human machine interface systems. Humans sometimes shall change something on machines. To do this they need an interface. These interfaces named as Human-Machine Interface(HMI). All devices from sensors to Programmable Logic Controllers(PLC) get and send commands or datas. They need to have a strong communication protocol to do this. CANBUS is which reliable communication protocol is the best option to accomodate this requirement.
Each step of producing industry devices must be communicate each other. Because timing and communicating is very important. All mechines have to wait each other and when one device finshed its work the other one has to start. A communicaton system must accomodate this. Also environmental variables also important at producing. Sensors send informations about environment to the central unit and it decide what to do.
So How CANBUS Works?
Variable data rates are specified, with 1Mbps data rate is the maximum and 10kbps the minimum rate. All modules must support 20kbps. Transmission distance is depends on the using data rate. Normally all the devices in a system transfer uniform and fixed bit-rates. The maximum line length is 1Km at lowest data rate, 50meters at 1Mbps. Termination resistors are placed at each all ends of the cables. Also inputs and output lines must be protected by zener diodes. For single ended lines a zenerwill connect to the GND. For the differential lines a zener diode is added both between the input and ground and the input and Vcc.
Components Of CAN Message Packet
- SOF: The Start of Message Frame. It says device will send a CAN Message now.
- CAN-ID: Specify the CAN message ID code in here lower ID values have higher priority
- RTR: The Remote Transmission Request indicates the communication between sub nodes
- Control: Inform the lenght of message (0-8 bits)
- Data: Contains the message values.
- CRC: The Cyclic Redundancy Check is used to ensure data transmitted correctly.
- ACK: This component specify the data transmitted correctly
- EOF: Says end of the message frame
That is all.
Have a good communicating.
Burak hamdi TUFAN