ABOUT PROJECT -> BUS
Bus (cable and connectors)
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The system bus is made of unshielded twisted pair cable category 5e. One pair is used for the CAN signal transmission, and two pairs supply power for nodes.
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UTP cat5e cable parameters according to Molex |
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| Wire Diameter | 24 AWG (0,51mm) | |||
| Max voltage | 125V | |||
| Max current | 1,5A | |||
| Resistance of isolation | >200MW | |||
| Resistance | 98W/km | |||
| Signal delay | ≤570ns/100m | |||
| Wave impedance | 100W | |||
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System has a bus topology. In practice it means that nodes are connected in chain as it is shown on a drawing. Current consumption must not exceed 1.5A, because of max UTP cable current.
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The bus must be terminated on both sides with resistor 120W. This eliminates signal reflections.
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As connectors RJ45 plugs and sockets are used.
1 - CAN H2 - CAN L 3 - not used 4 - CAN V+ 5 - CAN GND 6 - not used 7 - CAN GND 8 - CAN V+ |
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Maximum length of the bus is 500m when transmission speed is 125kbps. According to document DR-303-1 of CIA organisation (Can In Automation) it should be 150m when max of 100 nodes are connected. The maximum wiring length is given for different bus cables and different number of connected bus nodes in the following table.
| Wire cross-section[mm2] | Max bus length [m] | |||
| n=32 | n=64 | n=100 | ||
| 0.25 | 200 | 170 | 150 | |
| 0.5 | 360 | 310 | 270 | |
| 0.75 | 550 | 470 | 410 | |
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Maximum number of nodes on one bus must not exceed 112. This is because of max load allowed for CAN transceiver. It is possible to connect two or more buses together using bridges. Up to 112 nodes can be connected.
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Have a look at the flash animation showing the system bus. |
240kB |
