External crystal for CAN protocol

[Techman_7]

Why does external crystal needed / recommended for CAN communication ?
Can we use micrcocontroller internal oscillator for LIN communication instead of external crystal components?

 

[KlausST]

Hi,

The CAN bus nor the protocol does need a crystal.
It´s the CAN controller IC that needs it. --> Read the CAN controller IC datasheet about function and specifications.

Klaus

 

[Techman_7]

Hello,

I am asking for transcivers only not for protocol.
Question is for microcontroller CAN communication with & without crystal.

 

[KlausST]

Hi,

I am asking for transcivers only not for protocol.

Protocol: Your headline says "External crystal for CAN protocol"
Transceiver only: a pure CAN transceiver (PHY) does not need an XTAL either.

--> give a link to a datasheet and tell which chapter/page you refer to. Otherwise a further discussion of unelaborated questions makes no sense.

Klaus

 

[Techman_7]

Hello,

I am elaborating my question, for an embedded system with CAN interface I am using CAN transceiver.
Now, is it recommended to use external crystal for such system or internal oscillator (with the MCU) is sufficient?

CAN speed = 500 Kbps.

If we increase CAN data rate upto 5 Mbps (with CAN FD), then still internal oscillator is sufficient?

 

[KlausST]

--> give a link to a datasheet and tell which chapter/page you refer to. Otherwise a further discussion of unelaborated questions makes no sense.

 

[D.A.(Tony)Stewart]

Both CAN and LIN require a crystal or precision clock generator to derive the bit rate.

 

[Techman_7]

Thanks.

But, for LIN bitrate is less as compared to CAN.
LIN bitrate is around 20 kbps whereas for CAN its 500 Kbps or more.

So, still LIN required external crystal??

 

[D.A.(Tony)Stewart]

The Xtal can be scaled by counters and/or PLL to change the bit rate but the frequency tolerance error is defined for both must be met.
Slaves might be able to meet 16x or higher UART oversample tolerance error but not combined master and slave.

https://www.nxp.com/docs/en/application-note/AN5408.pdf

 

[FvM]

So, still LIN required external crystal??

Usually not. Refer to LIN spec. for detail requirements.

0.5% tolerance of master node needs a crystal clock, 14 % slave tolerance can be always achieved with internal oscillator, 1.5 % to 2 %, if required, can be critical over automotive temperature range.

CAN clock tolerance limits depends on several parameters, review respective application notes, usually internal oscillator isn't sufficient.

 

[Techman_7]

Both CAN and LIN require a crystal or precision clock generator to derive the bit rate.

If for LIN with speed of 20 kbps, internal oscillator is used then can the bit rate be derived from it ?? Or external crystal is must ?

 

[D.A.(Tony)Stewart]

Only if you can guarantee the error tolerances can be met between Tx and Rx

 

[FvM]

If for LIN with speed of 20 kbps, internal oscillator is used then can the bit rate be derived from it ?? Or external crystal is must ?

I conclude you decided not to bother with LIN synchronization feature? Happy developing!