At 09:26 PM 6/12/08, you wrote:
>The speedo wants 2,458 pulses per kilometre. This works out at dividing
>the wheel sensor frequency by about 2.367 with a maximum frequency from
>the wheels of 320Hz at 150MPH (no I don't plan to go that fast! Might as
>well design to the max speed though).

Express the 1/2.458 as a fractional binary number:

= 0.0110 1100 0010 0111 etc... or = 0.6C27 in hexadecimal

Now make a 16 bit variable, add 0x6C27 to it for every incoming 
pulse. Every time there is a carry set after addition, send an output 
pulse. The division ratio will be very close to 2.367 without large tables.

Best regards,

Josef

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