CAN Notes (4) Basic Concepts protocol
1. Basic Reference Model
The CAN protocol covers a predetermined OSI ISO 1 transport layer basic reference model, the physical layer and the data link layer
| The number of layers | ISO / OSI Basic Reference Model | The main project defined layers |
|---|---|---|
| Layer 7 | Application layer | Service can be used by the actual application |
| Level 6 | Presentation layer | Data conversion manifestations, such as: character set, data compression, encryption control |
| 5th floor | Session Layer | Correctly received and transmits to establish conversational communication, control data |
| 4th floor | Transport Layer | Sequence for controlling data transmission, the transmission error recovery, to ensure communication quality, such as: error correction, retransmission control |
| 3 layers | Network layer | Route selection data transfer or relay, such as: data exchange between the units, the address management |
| 2 layer | data link layer | The physical layer signal received (bit sequence) meaningful data, and the like to provide transmission error control data transfer control process, such as: access method, the form of data, communication connection control mode, the synchronous mode, the error detection mode and acknowledging packet (frame) bits constituting a modulation scheme (including bit timing condition) |
| 1 story | Physical Layer | The predetermined cable, connectors and the like medium used for electrical signal communication specification to enable signal transmission between devices, such as: a signal level, a transceiver, a cable, connector or the like form |
1 and the hardware control layer 2, the remainder of the control software
2. The definition of the basic reference model
CAN protocol on transport layer ISO / OSI basic reference model, the physical layer and the data link layer, which is defined as shown in the specific
| The number of layers | Defined matters | Features |
|---|---|---|
| Layer 4 (Transport Layer) | A retransmission control | Permanent try again |
| 2 layer (Logical Link Control LLC) | Select (may filter the received message) received message | You can point to point connection, broadcast, multicast |
| Overload notice | Ready to receive notification has not been completed | |
| Error Recovery | Resend | |
| Layer 2 (media access control MAC) | Message framing | Data frame, remote frame, the error frame, overload frame 4 Frame Type |
| Connection Control Mode | Competitive manner (support multicast) | |
| Arbitration when data conflicts | The arbitration, a higher priority ID may continue to be sent | |
| Fault diffusion restraint | Automatically determine a temporary error and error continued, troubleshooting node | |
| Error notification | CRC error, padding bit errors, bit errors, ACK error, format error | |
| Error detection | All units can be readily detected error | |
| Response mode | ACK, NACK two kinds | |
| Communication system | Hanso Engineering communication | |
| Layer 1 (physical signaling sublayer PLS) | Bit encoding | NRZ encoded NRZ, 6 bits inserted stuffing bits |
| Layer 1 (physical medium attachment PMD) | Bit Timing | Bit timing, the number of bits of the samples (user selection) |
| 1 layer (Medium Dependent receiving MDI) | Synchronously | Synchronization segment (SS) to achieve the synchronization (resynchronization function and having a) |
The data link layer is divided into
- Logical Link Control MAC (Logical Link Control) sub-layer
- Media Access Control LLC (Medium Access Control) sublayer
The MAC sublayer is the core of the CAN protocol
the data link layer is the physical layer signals from tissue is received into meaningful information, and to provide transmission error control and transmission flow control
Specifically, the message is the framing, arbitration, response, error detection or reporting
The data link layer are usually implemented in hardware in a CAN controller
in the physical layer defines the actual transmission mode signal, bit timing, and the synchronization bit encoding step
but specifically, the signal level, communication speed, sampling point, and the electrical characteristics of the bus driver, etc. undefined shape of the connector 2
which must be determined by a user itself according to system requirements
Reference:
"CAN Primer"
Related Recommendation:
CAN Notes (3) the error state
CAN Notes (2) CAN features
CAN Notes (1) CAN Introduction
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