CAN ( Controller Area Network ) RTLAB 김병철 08/03/20

개요 CAN 이란? AT91SAM7 의 CAN

CAN 이란? BOSCH 에서 자동차용 전자제어 장치들 간의 실시 간 통신을 위해 개발 ( Ex : ABS, 엔진관리, 변속관 리 ) CSMA/CD+AMP (carrier-sense multiple-access protocol with collision detection and arbitration on message priority) Simple 2-wire differential bus Bit rates up to 1Mbit/s 3종류의 CAN 버전 Four Frame Types Five Error Types Fault Confinement

CAN 계층 구조

CAN 노드 구조

CAN 적용 사례 6->7 : 2개의 Bus로 어떻게 데이터 통신을 하는가?

Bus Condition 뒤로 The Inverted Logic of a CAN Bus CANH와 CANL의 차가 0.5V 보다 작으면 Recessive ‘1’ 0.9V 보다 크면 Dominant ‘0’ 두개의 Bus값을 검사하여 다르면 “0” 같으면 “1” 뒤로

Bus Condition Bus에 대해 Dominant가 Recessive보다 우선순위가 높다!

CSMA/CD with AMP CSMA/CD with AMP (arbitration on message priority)

CAN Bit Coding & Bit Stuffing NRZ Bit Coding Stuff Bits are inserted after 5 consecutive bits of the same level for synchronization

CAN Bit Timing Configuration 뒤로

CAN Frame Formats CAN Versions Standard CAN ( V2.0A ) : 11-Bit Identifier Extended CAN ( V2.0B ) : 29-Bit Identifier Identifier = Priority

CAN Frame Formats 1Mbps의 속도로 data가 전송된다면 Standard의 경우 130us, Extended의 경우 154us의 시간이 소요된다.     1       start bit +  11     Identifier bit +  1       SRR bit +  1       IDE bit +  18     Identifier bit +  1       RTR bits +  6       Control bits +  64     Data bits +  15     CRC bits +  23     (maximum) Stuff bits +  1       CRC delimiter +  1       ACK slot +  1       ACK delimiter +  7       EOF bits +  3       IFS bits ------------------------------ =  154    bits     1       start bit +  11     Identifier bit +  1       RTR bits +  6       Control bits +  64     Data bits +  15     CRC bits +  19     (maximum) Stuff bits +  1       CRC delimiter +  1       ACK slot +  1       ACK delimiter +  7       EOF bits +  3       IFS bits ------------------------------ =  130    bits Standard Extended

Relation between BitRate and Bus Length

CAN Frame Formats Four Frame Types Data Frame (RTR=0) Remote Frame (RTR=1 and no data field) Error Frame (after violation frame format) Overload Frame (Not really used)

Error Detection Error Types CRC error Bit-stuffing error Bit error Form Error Acknowledgment error

Fault Confinement ERRA bit is set in the CAN_SR Register ERRP bit is set in the CAN_SR Register

AT91SAM7의 CAN CAN 2.0A and CAN 2.0B Bit rates up to 1Mbit/s 8 Mailboxes Also called channels or buffers The CPU reads or writes data via the CAN controller mailboxes Each mailbox has an ID Several mailboxes can be configured with the same ID Each can be Receive or Transmit one 16-bit Time Stamp

CAN Block Diagram

Mailbox Receive Mailbox Transmit Mailbox Mailbox with the lowest number is serviced first Mailbox Object Type Receive Receive with overwrite Consumer Transmit Mailbox Mailbox with the highest priority is serviced first Same priority -> mailbox with lowest number first Transmit Producer

Message Acceptance Procedure MIDx : Mailbox ID register MAMx : Acceptance Mask register

Message Acceptance Procedure

Receive Mailbox

Receive with Overwrite Mailbox

Chaining Receive Mailboxes All mailboxes are configured with same ID The mailbox with the largest number is configured in receive with overwrite mode (others are configured in receive mode)

Transmitting Messages

Producer/Consumer model

Producer / Consumer Handling

CAN Controller Timing Modes Timestamping Modes The value of the internal timer is captured at each Start Of Frame or each End Of Frame

CAN Controller Timing Modes Time Triggered Mode

CAN Controller Timing Modes Time Triggered Mode