EN 29/38
English
Manual
Limes LA50 / BA5
Absolute Magnetic Length Measurement System
Termination
Default setting: 0x01 (bus termination active)
CAN is a 2-wire bus system to which all partici-
pants are connected in parallel (i. e. with short
stub lines. The bus must be terminated at both
ends with a bus termination resistor of 120 (or
121) ohms in order to avoid reflections. This is
also necessary even for very short line lengths!
On the LA50, the CAN bus termination can be set by means of a rotary switch.
Since the CAN signals are represented on
the bus as differential levels, the CAN line
is comparatively insensitive to interference
(EMI). Interferences always affect both lines,
and therefore they almost do not modify the
differential level.
Bus length
With CAN, the maximum bus length is mainly limited by the signal propagation time. The
multimaster bus access procedure (arbitration) requires an almost simultaneous presence of
the signals (for the duration of one before scanning) at all nodes. Since the signal propagati-
on time is almost constant in the CAN connections (transceiver, optocoupler, CAN controller),
the line length must be adapted to the baud rate.
Baud-Rate
Bus length
1 MBit/s
< 20 m*
500 kBit/s
< 100 m
250kBit/s
< 250 m
125kBit/s
< 500 m
50 kBit/s
< 1000 m
20 kBit/s
< 2500 m
10 kBit/s
< 5000 m
*) the length of 40 m for 1 MBit/s is often
quoted in the literature for CAN. However, this
does not apply to networks with optodecou-
pled Can controllers. The worst-case calcu-
lation with optocouplers gives, for 1 MBit/s,
a maximum bus length of 5 m - experience
shows however that 20 m can be reached
without problem.
NOTICE!
For bus lengths exceeding
1000 m, the use of repeaters
may become necessary.
Summary of Contents for Limes BA5
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