At 03:08 PM 11/25/02 +0200, you wrote:

>I have written a algorith on the pic to mathematically convert the 10-bit
>number to a number between Ymin and Ymax but the algorithm takes far too
>long. Is there a way (hopefully easy) that you more or less can convert
>the 10-bit number to say between 100 and 200 almost directly (bit
>manipulation) without long and cumbersome arithmetic.

Nic,

One idea amounts to multiplying by (about) 25 and then dividing by 256
(throw away the LS byte).

Assuming you want 100-200 *inclusive*, you could do something like this
(I'll use pseudo-C code)

Let's assume x (one byte) contains the MS byte of the left-aligned A/D
value (0x00 to 0xFF as the A/D output
goes 0x000 to 0x3FF)

z = ((x + (x >> 1) >> 1) + (x >> 5) + (x >> 6);
                   ^^^^^^
         shift any carry from the addition in here

z= (z >> 1) + 100;


You'll recognize the shifts and adds as hard-coded multiplication.

This will reduce down to just a handful of PIC assembly instructions,
with no loops.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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