Suggested bit timing 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 µs | 16 | 14 | 87,5 % |
| 125 kbit/s | 500 m (2) | 8 µs | 16 | 14 | 87,5 % |
| 250 kbit/s | 250 m (2) | 4 µs | 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 µs | 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) on basis 5 ns/m propagation delay and a total effective ECU-internal (Elec. Control Unit) in-out delay as follows:
- 1M-800 kbit/s: 210ns
- 500 – 250 kbit/s: 300 ns (includes 2 * 40 ns for optocouplers)
- 124 kbit/s: 450 ns (includes 2 * 100 ns for optocouplers)
- 50 – 10 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 200 m the use of optocouplers is recommended. If optocouplers are placed between CAN controller and transceiver this affects the maximum bus length depending upon the propagation delay of the optocouplers
i.e. -4m per 10 ns propagation delay of employed optocoupler type.
Note 3: For bus length greater than about 1 km bridge or repeater devices may be needed.
