sug­gested bit timing and bus length

Bit­ti­ming as in CiA Draft Stan­dard 102 Ver­si­on 2.0

Bit rate (1)Bus lengthNomi­nal Bit timeNum­ber of
time quan­ta per bit
Loca­ti­on of sam­ple
point time quan­ta
Loca­ti­on of sam­ple point
per­cen­ta­ge
10 kbit/​s5000 m (3)100 µs161487,5 %
20 kbit/​s2500 m (3)50 µs161487,5 %
50 kbit/​s1000 m (3)20 µs161487,5 %
125 kbit/​s500 m (2)8 µs161487,5 %
250 kbit/​s250 m (2)4 µs161487,5 %
500 kbit/​s100 m2 µs161487,5 %
800 kbit/​s50 m1,25 µs10887,5 %
1 Mbit/​s25 m1 µs8687,5 %

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.