User:Dandudp/Editnotice

->The CAN bus (Controller Area Networking) was defined in the late 1980 by Bosch, initially for use in automotive applications. It has the following characteristics: l Uses a single terminated twisted pair cable l Is multi master l Maximum Signal frequency used is 1 Mbit/sec l Length is typically 40M at 1Mbit/sec up to 10KM at 5Kbits/sec l Has high reliability with extensive error checking l Typical maximum data rate achievable is 40KBytes/sec l Maximum latency of high priority message <120 μsec at 1Mbit/sec CAN is unusual in that the entities on the network, called nodes, are not given specific addresses. Instead, it is the messages themselves that have an identifier which also determines the messages' priority. For this reason there is no theoretical limit to the number of nodes although in practice it is ~64. Two specifications are in use: l 2.0A sometimes known as Basic or Standard CAN with 11 bit message identifiers which was originally specified to operated at a maximum frequency of 250Kbit/sec - ISO11519. l 2.0B known as Full CAN or extended frame CAN with 29 bit message identifier which can be used at up to 1Mbit/sec - ISO 11898. Nuts and Bolts From the systems and design viewpoint the detailed management of sending and receiving CAN messages will normally be done by dedicated hardware, on or off chip, (e.g. SJA1000) but an overview of these functions will be useful in order to design, setup and control a CAN system. Signal Characteristics CAN may be implemented over a number of physical media so long as the drivers are open-collector and each node can hear itself and others while transmitting (this is necessary for its message priority and error handling mechanisms). The most common media is a twisted pair 5v differential signal which will allow operations in high noise environments and with the right drivers will work even if one of the wires is open circuit. A number of transceiver chips are available the most popular probably being the Philips 82C251 as well as the TJA1040. When running Full CAN (ISO 11898-2) at its higher speeds it is necessary to terminate the bus at both ends with 120 Ohms. The resistors are not only there to prevent reflections but also to unload the open collector transceiver drivers.