AcroPack Series AP560
CAN Bus Interface Module
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This means that a bit stream of “1”
s
or “0”s appears continuous on the bus. A
logic “0” is called a dominant bit and a logic “1” is called a recessive bit.
Bit stuffing is used to ensure frequent enough transitions occur to achieve
synchronization. Every time a transmitter detects five consecutive bits of the
same polarity in the bit stream to be transmitted, it inserts a bit of opposite
polarity into the actual transmitted bit stream.
This bit stuffing rule applies to the Start-of-Frame field, arbitration field,
control field, data field and CRC sequence. The CRC delimiter, ACK field and
End-Of-Frame fields are of fixed form and not stuffed (see below for
definition of these fields). Furthermore, Error frames and Overload frames are
also of fixed form and not stuffed.
An example of how the bits in a stuffed bit stream might look is shown below.
00101011111
0
0000
1
1100000
1
11000
0 = dominant bit,
0
= dominant stuffed bit.
1 = recessive bit,
1
= recessive stuffed bit.
Message Frames
Standard Data Frame
The standard data frame is shown in Figure 2. The frame starts with a Start-of-
Frame (SOF) bit. This is a dominant bit that identifies the start of the data
frame on the bus.
The SOF is followed by the 12-bit arbitration field. The arbitration field
consists of an 11-bit identifier, ID28 - ID18, and the Remote Transmission
Request (RTR) bit. The RTR bit is used to distinguish between a data frame
(RTR bit dominant, logic 0) and a remote frame (RTR bit recessive, logic 1).
Following the arbitration field is the 6-bit control field. The first bit of the
control field is the Identifier Extension flag bit (IDE). This is used to distinguish
between standard and extended identifiers and must be dominant (logic 0)
for standard data frames. The next bit, r0, is specified by the CAN protocol as
a reserved bit for future expansion. This bit must be transmitted dominant,
but receivers must be capable of receiving either a dominant or recessive bit.
The final 4 bits of the control field make up the data length code (DLC. The
binary value of this 4-bit field specifies the number of data bytes in the data
payload (0 - 8 bytes). All binary combinations greater than or equal to
<1 0 0 0> specify 8 bytes of data.
After the control field is the data field, which contains a data payload equal to
the number of bytes specified by the DLC (see note above).
Содержание AcroPack AP560
Страница 28: ...AcroPack Series AP560 CAN Bus Interface Module 28 Figure 2 Standard Data Frame...
Страница 30: ...AcroPack Series AP560 CAN Bus Interface Module 30 Figure 3 Extended Data Frame...
Страница 32: ...AcroPack Series AP560 CAN Bus Interface Module 32 Figure 4 Remote Frame...
Страница 34: ...AcroPack Series AP560 CAN Bus Interface Module 34 Figure 5 Error Frame...
