Controller Area Network (CAN)

The Hytec CAN Eurocard product range includes a multi-function I/O Control board, a 16-input Intelligent 12-bit ADC board and an Intelligent CAN-PC Interface.

Hytec is currently developing a new modular range of intelligent CAN products for industrial control and data acquisition.

CAN Product Overview

Controller Area Network (CAN) is an ISO approved standard for a low cost real time communication protocol. It has a relatively high transmission speed (up to 1Mbps). It is fault tolerant and robust system.

CAN was initially developed by Robert Bosch for in-vehicle data transfer and was defined in 1984. Silicon became available in 1987 and CAN was first used in cars in 1992.The draft international standard was introduced in 1991 and this became a full standard (ISO 11898) in 1994.

CAN systems can be configured very efficiently and flexibly with respect to their data exchange. Many hardware features have been transferred to the software level. Its serial bus structure gives two advantages over parallel bus systems; increased transfer reliability even over large distances and more favourable costs. The serial bus usually consists of a single twisted pair. It has a multi-master priority based bus access which uses carrier sense multiple access with collision detection and non-destructive arbitration. (CSMA/CD + NDA). It has system wide data consistency.

CAN allows multicast reception with time synchronisation error detection and error signalling. It has automatic retransmission of corrupted messages and allows distinction between temporary errors and permanent failure of nodes with autonomous switch-off of defective nodes. A node can make a remote data request. Other features of CAN are functional addressing and automatic retransmission of corrupted messages. The signalling uses non-return to zero bit encoding and allows full isolation of the interconnecting wires. The standard covers the first two layers of the ISO OSI seven layer model, (physical and data link layers).

Performance facts

  • Topology: Bus configuration with only one logical bus line.
  • Transfer medium: Screened copper cable, also optical fibres.
  • Bus length: 40 metres at l Mbps to 500 metres at 125Kbps.
  • Transfer rate: 10 Kbps to 1 Mbps.
  • Data capacity: 0 to 8 bytes per message.
  • Number of identifiers: 2032 max.
  • Message length; 130 bits max.
  • System recovery time: Typically 17 - 23 bit periods, 29 bits max. after malfunction