Emp­foh­le­nes Bit­ti­ming und Buslänge

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.

Artikel wurde zuletzt editiert am Artikel wurde veröffentlicht am
12.01.2021 03.01.2017