Rainbow Electronics CAN интерфейс - Manual (Page 16)

BOSCH
ROBERT BOSCH GmbH, Postfach 50, D-7000 Stuttgart 1
Sep. 1991
Part A - page 14
IF CRCNXT THEN
CRC_RG(14:0) = CRC_RG(14:0) EXOR (4599hex);
ENDIF
UNTIL (CRC SEQUENCE starts or there is an ERROR condition)
After the transmission / reception of the last bit of the DATA FIELD, CRC_RG contains
the CRC sequence.
CRC DELIMITER
The CRC SEQUENCE is followed by the CRC DELIMITER which consists of a single
’recessive’ bit.
ACK FIELD
The ACK FIELD is two bits long and contains the ACK SLOT and the ACK DELIMITER.
In the ACK FIELD the transmitting station sends two ’recessive’ bits.
A RECEIVER which has received a valid message correctly, reports this to the
TRANSMITTER by sending a ’dominant’ bit during the ACK SLOT (it sends ’ACK’).
ACK SLOT
All stations having received the matching CRC SEQUENCE report this within the ACK
SLOT by superscribing the ’recessive’ bit of the TRANSMITTER by a ’dominant’ bit.
ACK DELIMITER
The ACK DELIMITER is the second bit of the ACK FIELD and has to be a ’recessive’
bit. As a consequence, the ACK SLOT is surrounded by two ’recessive’ bits (CRC
DELIMITER, ACK DELIMITER).
END OF FRAME
Each DATA FRAME and REMOTE FRAME is delimited by a flag sequence consisting
of seven ’recessive’ bits.
CRC
Field
ACK Slot
ACK Delimiter
End of
Frame
ACK FIELD
Data Frame