you wrote:

> >Here's an excerpt from a "comparison" tip page I'm working on:
>
> >Testing that a value lies within a range
>
> >In this example, the value in the W register will be tested to determine
> >whether it lies within the range specified by the constants loval and hival
> >(inclusive).  In other words, we're testing loval <= W <= hival.
>
> >        addlw   256-hival
> >        addlw   (hival-loval)+1
> >        btfsc   status,cf
> >        goto    inrange
>
>    Let's try this with w = 254, hival = 255, loval = 253.
>
>            254 + (256 - 255) = 255
>            255 + (255 - 253 + 1) = 258
>    which generates a carry.
>
>    Now try  w = 75, hival = 100, loval = 50
>
>            75 + (256 - 100) = 231
>            231 + (100 - 50 +1) = 252
>    which does not generate a carry.
>
>    In both cases the starting value is in range.   Did I miss something?
>

The quote code is a bit broken.

You want to :-

   1. Subtract the lo value, which should not generate a carry
   2. Subtract the difference, which should generate a carry

i.e.

    addlw 256-loval
    btfsc status,cf
    goto  outofrange
    addlw 256-(hival-loval)
    btfss status,cf
    goto  outofrange
inrange:

You will want +1's in various places depending on the range being >= or >
and <= or = the limits.

There is probably a way with one less goto by making the sums both generate
carry, and skip the second add if not set... but its too early in the
morning and I havn't had my cup of coffee yet.

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