Negative values

WILLQH

Hii,

· I am thinking of comparing the readings from my sensor to a preset reference value, and depending on the difference between the 2 values, the controller will determine an appropriate action. However, what will happen if the difference between the 2 values is a negative result ? Can Basic stamp 'recognise' the negative value ? For example I will like to have a algoritherm that goes something like : If value < = -1, GOSUB moveforward .. is it possible ?? Thank you.

Best regards

Bruce Bates

WILLQH -

The simple answer is - if you check your input values BEFORE doing any calculations, you can ensure that your result will always be positive. Ranging your values (upwards) may be required as well, just to ensure positive result numbers. What you do after the fact to get your final answer, is another matter entirely.

Although there is some intelligent processing of negative numbers with the PBASIC Stamp, you get into the area of two's complement notation, which becomes a quagmire for some folks, and thus should be avoided unless you're familiar with how they operate, and how to manipulate them.

Regards,

Bruce Bates

Martin Hebel

Negative numbers work well, except for a few things you need to watch for:
- Always use a Word sized variable
- Limits are +32,767 and -32,768
- When displaying, use SDEC
- If performing division, mod (//), and a few other math operations, this is the method I use:

BitSign var bit

BitSign = variable.Bit15 ' Save most significant bit, 1 = -, 0 = +
variable = (ABS variable) / 10 ' do math on absolute value
If BitSign = 1 THEN Variable = Variable * -1 ' re-apply sign by making negative

Hope this helps,
Martin

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<i>Electronic Systems Technologies
Southern Illinois University Carbondale

Personal Links - Lot of BASIC Stamp info

and

SelmaWare Solutions

StampPlot Pro Version 3 Release 4

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Now allows additional controls to be added, or developed.

Chris Savage

Thanks Martin.· Great information!· You can also get some information at Tracy Allen's website by going to the following link:

http://www.emesystems.com/BS2math4.htm#negatives

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Chris Savage
Parallax Tech Support
csavage@parallax.com