Recommended bittiming and bus length

Recommended bittiming and bus length

Recommended bitiming and bus length

Bittiming as in CiA Draft Standard 102 version 2.0

Bit rate(1)

Bus length

Nominal bit time

Number of
Time quanta per bit

Location of sample point time quanta

Location of sample point
percentage

10 kbit/s

5000 m(3)

100 μs

16

14

87.5%

20 kbit/s

2500 m(3)

50 μs

16

14

87.5%

50 kbit/s

1000 m(3)

20 us

16

14

87.5%

125 kbit/s

500 m(2)

8 us

16

14

87.5%

250 kbit/s

250 m(2)

4 us

16

14

87.5%

500 kbit/s

100 m

2 μs

16

14

87.5%

800 kbit/s

50 m

1.25 μs

10

8

80%

1 Mbit/s

25 m

1 us

8

6

75%

Oscillator frequency: 16 MHz +/-0.1% (1000 ppm)
Sampling mode: Single sampling SAM = 0
Synchronization mode: Recessive to dominant edges only SYNC = 0
Synchronization jump width: 1 * tq SJW = 0
Phase segment 2: 2 * tq TSEG2 = 1

Note 1: Rounded bus length estimation (worst case) based on 5 ns/m propagation delay and a totally effective ECU-internal (Elec. Control Unit) in-out delay as follows:

  1. 1M-800 kbit/s: 210ns
  2. 500 🙂 250 kbit/s: 300 ns (including 2 * 40 ns for optocouplers)
  3. 124 kbit/s: 450 ns (including 2 * 100 ns for optocouplers)
  4. 50 kbit/s: 1.5 tq; Effective delay = delay recessive to dominant plus dominant to recessive divided by two.

Note 2: For bus length greater than about 200m the use of optocouplers is recommended. If optocouplers are placed between CAN controller and transceiver this affects the maximum bus length depending on the propagation delay of the optocouplers

i.e.‐4m per 10 ns propagation delay of used optocoupler type.

Note 3For bus length greater than about 1 km bridge or repeater devices may be needed.