Rainbow Electronics CAN интерфейс - Manual (Page 13)

BOSCH
ROBERT BOSCH GmbH, Postfach 50, D-7000 Stuttgart 1
Sep. 1991
Part A - page 11
START OF FRAME
marks the beginning of DATA FRAMES and REMOTE FRAMEs. It consists of a single
’dominant’ bit.
A station is only allowed to start transmission when the bus is idle (see BUS IDLE). All
stations have to synchronize to the leading edge caused by START OF FRAME (see
’HARD SYNCHRONIZATION’) of the station starting transmission first.
ARBITRATION FIELD
The ARBITRATION FIELD consists of the IDENTIFIER and the RTR-BIT.
IDENTIFIER
The IDENTIFIER’s length is 11 bits. These bits are transmitted in the order from ID-10
to ID-0. The least significant bit is ID-0. The 7 most significant bits (ID-10 - ID-4) must
not be all ’recessive’.
RTR BIT
Remote Transmission Request BIT
In DATA FRAMEs the RTR BIT has to be ’dominant’. Within a REMOTE FRAME the
RTR BIT has to be ’recessive’.
CONTROL FIELD
The CONTROL FIELD consists of six bits. It includes the DATA LENGTH CODE and
two bits reserved for future expansion. The reserved bits have to be sent ’dominant’.
Receivers accept ’dominant’ and ’recessive’ bits in all combinations.
DATA LENGTH CODE
The number of bytes in the DATA FIELD is indicated by the DATA LENGTH CODE.
This DATA LENGTH CODE is 4 bits wide and is transmitted within the CONTROL
FIELD.
Interframe
Space
Start
of Frame
Identifier
RTR Bit
Control
Field ARBITRATION FIELD
Data Frame