docs: Add notes on terminating resistors to CANBUS.md
Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
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@ -6,10 +6,9 @@ Klipper currently only supports CAN on stm32 chips. In addition, the
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micro-controller chip must support CAN and it must be on a board that
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has a CAN transceiver.
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To compile for CAN, run "make menuconfig", unselect "Use USB for
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communication (instead of serial)" and then select "Use CAN for
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communication (instead of serial)". Finally, compile the
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micro-controller code and flash it to the target board.
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To compile for CAN, run "make menuconfig" and select "CAN bus" as the
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communication interface. Finally, compile the micro-controller code
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and flash it to the target board.
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# Host Hardware
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@ -41,6 +40,24 @@ iface can0 can static
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Note that the "Raspberry Pi CAN hat" also requires [changes to
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config.txt](https://www.waveshare.com/wiki/RS485_CAN_HAT).
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# Terminating Resistors
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A CAN bus should have two 120 ohm resistors between the CANH and CANL
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wires. Ideally, one resistor located at each the end of the bus.
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Note that some devices have a builtin 120 ohm resistor (for example,
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the "Waveshare Raspberry Pi CAN hat" has a soldered on resistor that
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can not be easily removed). Some devices do not include a resistor at
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all. Other devices have a mechanism to select the resistor (typically
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by connecting a "pin jumper"). Be sure to check the schematics of all
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devices on the CAN bus to verify that there are two and only two 120
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Ohm resistors on the bus.
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To test that the resistors are correct, one can remove power to the
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printer and use a multi-meter to check the resistance between the CANH
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and CANL wires - it should report ~60 ohms on a correctly wired CAN
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bus.
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# Finding the canbus_uuid for new micro-controllers
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Each micro-controller on the CAN bus is assigned a unique id based on
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