AN1105 datasheet(9/100 Pages) STMICROELECTRONICS

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ST7 pCAN PERIPHERAL DRIVER

transmission of a dominant bit forces this state to dominant, no matter how many other nodes

are transmitting recessive bits.

1.3.1 Bit Stuffing

Once built, a frame is passed to the Transfer sub-layer, where the CRC is calculated. Then,

Stuffing Bits are inserted in the frame. Each time five consecutive bits of the same logical

level are detected, a bit of the opposite value is inserted. This is used to generate a minimum

edge rate on the bus for resynchronisation purpose (See “Bit timing” on page 9).

Figure 5. Bit-stream NRZ Code & Bit Stuffing

1.3.2 Bit timing

The CAN standard divides the bit time into four segments:

– A synchronisation segment (SYNC),

– A propagation segment (PROP),

– A phase buffer 1 segment (TSEG1),

– A phase buffer 2 segment (TSEG2),

– Each segment is divided into time quanta. The synchronisation segment lasts, by defini-

tion, 1 time quantum.

Figure 6. CAN Bit Segments

The CAN communication is asynchronous, i.e. no clock signal is sent together with data. Each

node in the network maintains its own bit timing calculated from the internal clock of the de-

vice.

1 0 1 1 1 0 1 0 1 0 0 0 0 0 1 0 0 0 1 1 0 1 1 1 1 1 0 0 0 1

Stuff bits

SYNC

PROP

TSEG1

Bit Time

Sample Point

TSEG2

Next Bit

Bit

AN1105 Folha de dados(PDF) 9 Page - STMicroelectronics