BOSCH CAN Specification Version 2.0 1991, Robert Bosch GmbH, Postfach 50, D-7000 Stuttgart 1 Thi dtt dith FM k4 0 4 The document as a whole may be copied and distributed without restrictions. However, the usage of it in parts or as a whole in other documents needs the consent of Robert Bosch GmbH. Robert Bosch GmbH retains the right to make changes to this document without notice and does not accept any liability for errors. Imported into Framemaker 4 by: Chuck Powers, Motorola MCTG Multiplex Applications, April 5,1995. BOSCH ROBERT BOSCH GmbH, Postfach 300240, D-7000 Stuttgart 30 Sep. 1991 page 1 Recital The acceptance and introduction of serial communication to more and more applications has led to requirements that the assignment of message identifiers to communication functions be standardized for certain applications. These applications can be realized with CAN more comfortably, if the address range that originally has been defined by 11 identifier bits is enlarged Therefore a second message format (extended format) is introduced that provides a larger address range defined by 29 bits. This will relieve the system designer from compromises with respect to defining well-structured naming schemes. Users of CAN who do not need the identifier range offered by the extended format, can rely on the conventional 11 bit identifier range (standard format) further on. In this case they can make use of the CAN implementations that are already available on the market, or of new controllers that implement both formats. In order to distinguish standard and extended format the first reserved bit of the CAN message format, as it is defined in CAN Specification 1.2, is used. This is done in such a way that the message format in CAN Specification 1.2 is equivalent to the standard format and therefore is still valid. Furthermore, the extended format has been defined so that messages in standard format and extended format can coexist within the same network. This CAN Specification consists of two parts, with Part A describing the CAN message format as it is defined in CAN Specification 1.2; Part B describing both standard and extended message formats. In order to be compatible with this CAN Specification 2.0 it is required that a CAN implementation be compatible with either Part A or Part B. Note CAN implementations that are designed according to part A of this or according to previous CAN Specifications, and CAN implementations that are designed according to part B of this specification can communicate with each other as long as it is not made use of the extended format. CAN Specification 2.0 PART A BOSCH ROBERT BOSCH GmbH, Postfach 50, D-7000 Stuttgart 1 Sep. 1991 Part A - page 3 1INTRODUCTION4 2BASIC CONCEPTS5 3MESSAGE TRANSFER.10 3.1Frame Types10 3.1.1DATA FRAME10 3.1.2REMOTE FRAME 15 3.1.3ERROR FRAME.16 3.1.4OVERLOAD FRAME17 3.1.5INTERFRAME SPACING.18 3.2Definition of TRANSMITTER/RECEIVER 20 4MESSAGE VALIDATION.21 5CODING.22 6ERROR HANDLING.23 6.1Error Detection.23 6.2Error Signalling.23 7FAULT CONFINEMENT.24 8BIT TIMING REQUIREMENTS27 9INCREASING CAN OSCILLATOR TOLERANCE31 9.1Protocol Modifications31 Contents BOSCH ROBERT BOSCH GmbH, Postfach 50, D-7000 Stuttgart 1 Sep. 1991 Part A - page 4 1 INTRODUCTION The Controller Area Network (CAN) is a serial communications protocol which efficiently supports distributed realtime control with a very high level of security. Its domain of application ranges from high speed networks to low cost multiplex wiring. In automotive electronics, engine control units, sensors, anti-skid-systems, etc. are connected using CAN with bitrates up to 1 Mbit/s. At the same time it is cost effective to build into vehicle body electronics, e.g. lamp clusters, electric windows etc. to replace the wiring harness otherwise required. The intention of this specification is to achieve compatibility between any two CAN implementations. Compatibility, however, has different aspects regarding e.g. electrical features and the interpretation of data to be transferred. To achieve design transparency and implementation flexibility CAN has been subdivided into different layers. the (CAN-) object layer the (CAN-) transfer layer the physical layer The object layer and the transfer layer comprise all services and functions of the data link layer defined by the ISO/OSI model. The scope of the object layer includes finding which messages are to be transmitted deciding which messages received by the transfer layer are actually to be used, providing an interface to the application layer related hardware. There is much freedom in defining object handling. The scope of the transfer layer mainly is the transfer protocol, i.e. controlling the framing, performing arbitration, error checking, error signalling and fault confinement. Within the transfer layer it is decided whether the bus is free for starting a new transmission or whether a reception is just starting. Also some general features of the bit timing