Re: CANBus Baud Rates

Bryan Armstrong wrote:

> Vic wrote:
>
>> Does changing the crystal affect the clock,
>> performance or other parts of TINI's operation?
>
>
> Yes, the CPU will be slower.  Some baud rates on serial ports may be 
> unattainable without lots of bit error.
>
>> Instead of 14Mhz could I change to 18Mhz.
>
>
> Yes, but you will need to recalculate the critical timing parameters 
> of your RAM and Flash to make sure they will not be violated when the 
> frequency goes up.
>
>> Why was 18.432Mhz chosen in the first place, if its
>> known to cause CAN speed issues. Is there a specific
>> subsystem that requires such frequency for proper
>> operation?
>
>
> 18.432MHz is what we call a "baud rate crystal".  Pick any baud rate 
> and divide into 18.432MHz and you will always get a whole number (i.e. 
> zero bit error).  Other good baud rate crystals are: 11.0592, 14.7456, 
> 22.1184 and multiples of these.
>
>
I removed the crystal from my TINI and soldered in two pins that I 
removed from a turned-pin IC socket. I swap between a 20MHz (for CAN) 
and 18.432MHz (the original) crystal. I use the 18.432 with the JavaKit. 
I have never tried programmed the FLASH while using the 20MHz crystal.

My TINI is an older Rev. G board with 80C390 CPU, at 20MHz it may be 
slightly over clocked but works fine. The Ethernet interface has its own 
20MHz crystal so is independant of CPU crystal.

Regards
Andrew


_______________________________________________
TINI mailing list
TINI-6tN4nzCoH/[email protected]
To UNSUBSCRIBE, edit your profile, or see list archives:
http://lists.dalsemi.com/mailman/listinfo/tini