CM0504 User Guide
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The•CAN•cable•is•very•susceptible•to•system•noise;•therefore,•CAN•shield•must•be•connected•as•
follows:
a.•
Connect•CAN•Shield•to•the•point•of•least•electrical•noise•on•the•CAN•bus.
b.• Connect•CAN•Shield•as•close•to•the•center•of•the•CAN•bus•as•possible.
c.•
Use•the•lowest•impedance•connection•possible.
Note:
•Ground•loops•can•damage•electronic•modules.•The•CAN•Shield•can•only•be•grounded•to•one•point•
on•the•network.•If•grounded•to•multiple•points,•a•ground•loop•may•occur.
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CAN•Connectors:•Industry-approved•CAN•connectors•are•manufactured•by•ITT•Cannon•and•
Deutsch,•and•come•in•either•T•or•Y•configurations.•
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CAN•Harness:•The•CAN•harness•is•the•main•backbone•cable•that•is•used•to•connect•the•CAN•network.•
This•cable•cannot•be•longer•than•40•meters•and•must•have•a•120•Ω•terminating•resistor•at•each•end.•
The•120•Ω•terminating•resistors•eliminate•bus•reflections•and•ensure•proper•idle-state•voltage•levels.
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CAN•Stubs:•The•CAN•stubs•cannot•be•longer•than•1•meter,•and•each•stub•should•vary•in•length•to•
eliminate•bus•reflections•and•ensure•proper•idle•state•voltage•levels.
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Max•Number•of•Modules•in•a•System:•The•CAN•bus•can•handle•a•maximum•of•30•modules•in•a•
system•at•one•time.
The•following•shows•a•typical•CAN•connection•using•the•SAE•J1939•standard:
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120 ohm
Terminator
120 ohm
Terminator
Node
Node
Node
Node
Node
T connectors
Variable length
CAN stub (<1m)
CAN Network Backbone
(less than 40 meters long)
Figure 7.1. J1939 CAN connection