Civil Engineering Reference
In-Depth Information
Table 4.1
Location of sampling point for several bit rates
Bit rate
Nominal bit time t
b
(µs)
Valid range for location
of sample point (%)
Recommendation location
of sample point (%)
1 Mbit/s
1
75-90
87.5
800 kbit/s
1.25
75-90
87.5
500 kbit/s
2
85-90
87.5
250 kbit/s
4
85-90
87.5
125 kbit/s
8
85-90
87.5
50 kbit/s
20
85-90
87.5
20 kbit/s
50
85-90
87.5
10 kbit/s
100
85-90
87.5
Table 4.2
Maximal
recommended bus and stub length
Bit rate
Bus length (m)
Stub length (max; m)
Accumulated stub
length (max; m)
1 Mbit/s
25
1.5
7.5
800 kbit/s
50
2.5
12.5
500 kbit/s
100
5.5
27.5
250 kbit/s
250
11
55
125 kbit/s
500
22
110
50 kbit/s
1,000
55
275
20 kbit/s
2,500
137.5
687.5
10 kbit/s
5,000
275
1,375
Originally, CANopen was considered for usage in “embedded” networks in ma-
chine control systems. Meanwhile CANopen is used in a variety of industrial sec-
tors as an “embedded” communication system. This also includes particular special
purpose vehicles, trains, lifts and medical devices (e.g. computed tomography (CT)
scanners) as well as ships.
4.1.1
Profiles for the Lower Layers
Currently, CANopen uses mainly the physical transmission according to ISO
11898-2. Alternative physical interfaces (ISO 11898-3 and Powerline) are being de-
veloped for specific applications. However, the bit timing is not explicitly specified
in ISO 11898-1 and ISO 11898-2. Out of this reason, the CANopen communication
profile (EN 50325-4 respectively CiA 301) defines sample points for several bit
rates. Table
4.1
shows an overview of the bit timing parameters. Other bit rates are
not allowed. Bit rates less than 50 kbit/s are not supported by all Controller Area
Network (CAN) transceivers.
Table
4.2
shows the achievable bus length, on the basis of the recommended
sample points, if direct current (DC) and alternating current (AC) voltage param-
eters for cables and connectors compliant to ISO 11898-2 are used. The actual
