CAN is based on a broadcast communication mechanism. This broadcast communication is achieved by using a message oriented transmission protocol. These messages are identified by using a message identifier. The message identifier has to be unique within the whole network and it defines not only the content but also the priority of the message.

The CAN data link layer comprises two protocols: Classical CAN introduced in 1986 and CAN FD introduced in 2012. The protocols are internationally standardized in ISO 11898-1:2015. Both protocols support base frames (11-bit CAN-ID) and extended frames (29-bit CAN-ID), leading to four message frame formats:

Classical base frame format (CBFF): message that contains up to 8 byte and is identified by 11 bits
Classical extended frame format (CEFF): message that contains up to 8 byte and is identified by 29 bits
FD base frame format (FBFF): message that contains up to 64 byte and is identified by 11 bits
FD extended frame format (FEFF): message that contains up to 64 byte and is identified by 29 bits

The Classical CAN protocol uses one bit-rate in the arbitration and the data phase. The transmission speed is limited to 1 Mbit/s. The payload (i.e. the data field) is limited to 8 byte. The following picture shows a Classic CAN frame with an 11-bit CAN-ID.

Classic CAN frame

The CAN FD protocol allows payloads up to 64 byte. Additionally, it supports an optional second bit-rate for the data-phase (field BRS). The following picture shows a CAN FD frame with an 11-bit CAN-ID.

CAN FD frame

Programming in C

canpie.h	CANpie FD definitions
cp_core.h	CANpie FD core functions
cp_fifo.h	CANpie FD FIFO functions
cp_msg.h	CANpie FD message access functions

Programming in C++

The CANpie FD API provides classes for manipulation of CAN frames and passing these frames via a socket interface (QCanSocket) between applications.

The classes are using the Qt Library and have the prefix QCan. The following table gives an overview.

QCanFrame	Class defining a CAN data frame or error frame
QCanInterface	Class defining a physical CAN interface
QCanNetwork	Class defining a CAN network
QCanNetworkSettings	Access parameters of QCanNetwork
QCanPlugin	Class for a CAN plugin, used by the QCanServer
QCanServer	CANpie server class, managing multiple CAN networks
QCanServerSettings	Access parameters of QCanServer
QCanSocket	Class defining a CAN socket, which connects to a QCanNetwork
QCanSocketCpFD	CANpie FD interface for QCanSocket class
QCanSocketDialog	Dialog for QCanSocket class
QCanTimeStamp	Time-stamp with a resolution of 1 nanosecond.