How to detect variable going below zero, without using PBPL ?

[richard]

But if ADC value gets below 150, then things get bad.

what does get bad mean ?

show your code

[CuriousOne]

Variable value should go to negative, but since we have no negative, it goes into 65xxx range

[richard]

Variable value should go to negative, but since we have no negative, it goes into 65xxx range

only if you interpret it incorrectly and ignore the sign bit



show your code

[CuriousOne]

So by checking the last bit, I can know, whenever variable went into negative world, right?

[Ioannis]

That is what post #3 says. Henrik explained it well.

Ioannis

[mpgmike]

Whether signed or unsigned, 0 = 0.
With an Unsigned BYTE (let's start simple), the range is 0 to 255. From 255, add 1 and you get 0 again, as the BYTE rolls over.
With a Signed BYTE, the range is -128 to +127. Think in terms of binary: 127d = %0111 1111. Make sense so far?

Working with a Signed BYTE, if you calculate: "0 - 1 =", you get %1111 1111 which equals -1.
With an Unsigned BYTE, if you calculate: "0 - 1 =" you still get %1111 1111, but it equals 255.

Think about this for Signed Variables:
0d = %0000 0000
1d = %0000 0001
-1d = %1111 1111
-2d = %1111 1110

Sometimes just looking at the representations enables the light bulb to turn on.

Now if we're working at the 16-bit WORD level:
0d = %0000 0000 0000 0000
1d = %0000 0000 0000 0001
-1d = %1111 1111 1111 1111
-2d = %1111 1111 1111 1110

See the trend?? I hope this helps you figure some things out.

[richard]

its called two's compliment , no magic involved

https://en.wikipedia.org/wiki/Two%27s_complement