Horner APG RCS SmartStix - Manual (Page 28)

PAGE 28 15 MAR 2003 CH.2
MAN0305-04
Figure 2.16 – CAN Wiring
Note: To optimize CAN network reliability in electrically noisy environments, the CAN power
supply needs to be isolated (dedicated) from the primary power.
a.
CAN Wiring Rules (See Figure 2.16.)
1.
Wire the CAN network in a daisy-chained fashion such that there are exactly two physical end-
points on the network.
2. The two nodes at the physical end-points need to have 121 ohm 1% terminating resistors
connected across the CN_L and CN_H terminals.
3. Use data conductors (CN_L and CN_H) that are 24 AWG shielded twisted pair for “thin cable” and
22 AWG shielded twisted pair for “thick cable.” They must also have 120-ohm characteristic
impedance. In typical industrial environments, use a Belden wire #3084A (“thin”). Use #3082A
(“thick”) for network cable lengths greater than 100 meters environments where noise is a concern.
Place data conductors (CN_L and CN_H) into a twisted pair together.
4. Use power conductors (V- and V+) that are 18 AWG twisted-pair for “thin cable” and 15 AWG
twisted-pair for “thick cable.” Place power conductors (V- and V+) into a twisted pair together.
5. If local codes require the local CAN power supply to be earth grounded, connect the V- power
conductor to a good earth ground at one place only on the network, preferably at a physical
endpoint. If multiple power supplies are used, only one power supply must have V- connected to
earth ground. The remaining power supplies need to be isolated.
121 Ω
V
-
C
N
_
L
S
H
IE
L
D
C
N
_
H
V
+
V
-
C
N
_
L
S
H
IE
L
D
C
N
_
H
V
+
V
-
C
N
_
L
S
H
IE
L
D
C
N
_
H
V
+
121 Ω
V
-
C
N
_
L
S
H
IE
L
D
C
N
_
H
V
+
12-25VDC
+
-
RED
WHT
SHIELD
BLU
BLK
R
E
D
S
H
IE
L
D
RED
WHT
BLU
BLK
V
+
C
N
_
L
V
-
S
H
IE
L
D
1
2
1
Ω
C
N
_
H
V
+
C
N
_
L
V
-
S
H
IE
L
D
C
N
_
H
R
E
D
W
H
T
B
L
U
B
L
K 1
2
1
Ω
V
+
C
N
_
L
V
-
S
H
IE
L
D
C
N
_
H
R
E
D
W
H
T
B
L
U
B
L
K
RED
WHT
SHIELD
BLU
BLK
RED
WHT
BLU
BLK
V
+
C
N
_
L
V
-
S
H
IE
L
D
C
N
_
H
12-25VDC
+
-