Siemens MICROMASTER 420 Operating Instructions Manual page 71

Issue 01/05
Cable lengths
The lengths of the bus cables in a CANopen network depend on the baud rate and
the delay times of the various nodes.
The maximum cable lengths for a CANopen network with a CANopen master and a
MICROMASTER 420/430/440 are calculated in the following example. It is as-
sumed that the CANopen MASTER has the same delay times as MICROMASTER
420/430/440.
When calculating the maximum cable lengths between the two nodes located the
farthest away from each other, it is decisive that the nodes with the highest delay
are also located at the start and at the end of the network. Another calculation must
be made if a node with even higher delay times is to be located in a network.
T
Optocoupler
T
Transceiver
T
CAN
Node 1
Fig. 4-5 CANopen network with delay times
T
CAN
T
Transceiver
T
Optocoupler
T
Ltg
L
max
The maximum length of cable between two nodes is calculated using the formula
below:
⋅
2 Baudrate
L =
max
0,85
⋅
2 Baudrate
CANopen Option Module Operating Instructions
6SE6400-5BC00-0BP0
L
max
CAN bus cable
T
Ltg
Optocoupler
Transceiver
CAN-Controller
Time lag of the CAN interface chip
Time lag of the transceiver element
Time lag of the opto-coupler
Time lag of the cable
Maximum length of cable
0,85
- T
el
=
T
Ltg
+ +
- ([T In out] [T
CAN Transceive
T
Ltg
Information for the CANopen master
Node 2
+ + ⋅
Tx Rx] [2 T
r Optocouple r
T
Optocoupler
T
Transceiver
T
CAN
])
71