Re: TouCAN too slow by 2X?

Back then, I had missed a half-speed feature - I think were driving the
external bus at half-speed:

		8.5.2 Clock Out (CLKOUT)
		CLKOUT has the same frequency as the general system
clock (GCLK2_50). Unlike the main system clock
		GCLK1/GCLK2 however, CLKOUT (and GCLK2_50) represents
the external bus clock, and thus will be
		one-half of the main system clock if the external bus is
running at half speed (EBDF = 0b01). The
		CLKOUT frequency (system frequency) defaults to VCO/2.
		

With a 40 MHz clock, I used CANbus prescaler dividers of 2,4,8 or 16
and 20 Tq/bit for 1 MBPS, 500, 250 or 125.

With a 56 MHz clock, I think you need to get a factor of 7 into the
prescaler, i.e. bring 56 MHz down to 8 MHz, but can you still get 1
MBPS? 

Check the minimum allowable values of the segments, and where your
sample point needs to fall - these may not be legal or workable values,
but are a starting point:

divide by 7
56 -->  8 MHz ~ 125 ns
Want 8 Tq per bit

 SynchSeg + (PROPSEG+1) + (PSEG1+1) + (PSEG2+1) = 
     1    +      4      +      1    +     2     =  8 time quanta per bit

Rick Corey

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