LPC4088 QuickStart Board - How to Expand - CAN
There are two CAN interfaces on the LPC4088 QuickStart Board. The CAN interface is perfect for communication between separate controllers over long distance (in harsh environments). Multiple devices can connect to one CAN bus.
- CAN1 is available on p9/p10.
- CAN2 is available on p33/p34.
The advantages of the CAN bus are:
- Medium speed communication, up to 1 Mbps (for distances up to 40 meters).
- Long bus length supported (several hundred meters - but a longer bus require lower bit rate).
- Differential signaling improves noise immunity.
- Arbitration and Acknowledgement included in protocol.
- Only two wires needed.
- 11-bit adressing scheme.
The disadvantages are:
- Requires external transceiver.
- Relatively low bit rate, especially over longer distances.
For more information about CAN, see http://en.wikipedia.org/wiki/Controller_area_network
The thwo CAN busses can be used simultaneously. One CAN bus can be shared by different parts of the application program, for example when running several processes/tasks in an RTOS (Real-Time Operating System). Some kind of mutual-exclusive protection or driver abstraction must then be created so that the use of the bus is serialized in time, i.e., two or more users do not try to use the bus simultaneously.
On the other hand, using separate CAN busses can make the program control simpler. Separate parts of the program can control separate CAN busses.
One page covers example CAN expansion in the example interface design schematic. An external CAN tranceiver is needed and the NXP TJF1051T/3 chip is used as example but there are many other CAN tranceivers that can be used.
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