# Cannot start CAN2

**URL:** <https://forum.opencyphal.org/t/cannot-start-can2/494>\
**Category:** Applications & Usage\
**Created:** [May 27, 2019, 7:16pm UTC](https://forum.opencyphal.org/t/cannot-start-can2/494 "2019-05-27T19:16:26Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Sergey\_Frolov](https://forum.opencyphal.org/letter_avatar_proxy/v4/letter/s/b19c9b/32.png) [@Sergey\_Frolov](https://forum.opencyphal.org/u/Sergey_Frolov)\
**Post date:** [May 27, 2019, 7:16pm UTC](https://forum.opencyphal.org/t/cannot-start-can2/494/1 "2019-05-27T19:16:27Z")

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Hello.  
I’m building application with PX4. And uavcannode works fine with CAN1 (if NUM\_IFACES=1). But, if I define CAN2 (and NUM\_IFACES=2) all uavcannode doesnt works. No CAN 1 and CAN2 both.  
But both of them must start. I think, this trouble caused, that CAN1 cannot start correctly (no connected line to it). And of course CAN2 also go to fail.  
Right?

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**Author:** ![pavel.kirienko](https://forum.opencyphal.org/user_avatar/forum.opencyphal.org/pavel.kirienko/32/9_2.png) [@pavel.kirienko](https://forum.opencyphal.org/u/pavel.kirienko)\
**Post date:** [May 31, 2019, 8:23am UTC](https://forum.opencyphal.org/t/cannot-start-can2/494/2 "2019-05-31T08:23:26Z")

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> [@Sergey\_Frolov](#):
>
> I think, this trouble caused, that CAN1 cannot start correctly (no connected line to it). And of course CAN2 also go to fail.  
> Right?

I assume that when you say that there is no connected line you mean that there is no CAN driver connected to the CAN1 interface. If this assumption is correct then it makes sense. Something must pull the CAN\_RX line towards the recessive level in order for the controller to initialize successfully.