Picaxe math restriction

[rbright]

Pixaxe will only allow integer calculation and then only with values less than 65535.

I'm trying to process some negative temperature values from a DS18B20 and I need to divide by a fraction as follows:

I have 16 bit word W1 which contains FF5E. I want to subtract that from FFFF then divide the result by 0.0625.

Any ideas

 

[centrex]

Have a look at the following it works:
http://www.phanderson.com/picaxe/ds18b20_08m.html

 

[MPep]

Do a forum search.
I found the following

It's will return anything between -55 to 125ºc

The positive values will be returned directly such as b1 = 25

The negative values will be everything bigger than 127. In this case, you'll have to substract 128 from this value.

Having that, you can have something like.

b1 = 140

So, b1 = 140 - 128

Then b1 = 12

That means you have -12ºc

Okay, this is for 8bits only but you get the idea.

2's complement is used here.

 

[westaust55]

Have a read at this thread as well
http://www.picaxeforum.co.uk/showthread.php?t=13354&highlight=DS18B20

The maths for the 12bit mode of calculation for the DS18B20 covering positive and negative has been posted on this forum several times before for those who wish to search.

 

[rbright]

Now Working - see other post today

Thanks for the hints to use 2's Compliment - of course that is what the DS18B20 was expecting to have to process it's negative values. I've just posted on another thread the resulting code as a bit of a tutorial for others but with lots of comments