Reading Array values into variables

[Tom Gonser]

Seems like I should be able to figure this out, but I can't ...

I have an array that contains 24 bits which equate to an altitude in tenths of meters.

alt[1]
alt[2]
alt[3]


I need to 1) display this, and 2) convert from meters to feet, so I need to stuff all these into a single variable which represents actual meters as opposed to tenths of meters, then convert to feet....

Any ideas out there? They way I am doing it now is not working. I am just reading these into alt1, alt2, alt2, and showing them as #alt1, #alt2, #alt3... I get 13130 which may be 131.30 meters,(which would be about right) but I am not sure. I am also not sure how to make this a single variable ..

Thanks !

Tom

[Demon]

I have no answer, but I do see an immediate problem.

A byte contains 8 bits, a word contains 2 bytes; that's a total of 16 bits.

There is a way to do 32 bit math, I saw a section in the manual. You work with 2 separate words or something, I didn't pay much attention.

Robert

[Demon]

Page 33, 4.17.1 - Multiplication.

Using * and **, / and //.

Good luck!

Robert

[Tom Gonser]

Exactly the problem.. I have 3 bytes that need to be put into one variable.. this is a 24 bit container that relates a number - the altitude in tenths of meters..

How to get this into ONE variable I can work with is the first issue..

Tom

[Acetronics2]

Hi, Tom

Let's have another view of the problem ...

You get an altitude measurement, ...but what is your sensor ??? and mostly what is its precision ???

I do not know lots of altitude sensors seriously able to give 1 cm on a hundred meters ... 1/10 000 precision, you sure ??? ... !!!

May be a little look here could reduce your number sizes ...and simplify you work.

24 and 32 bits arithmetics can be downloded from Melabs site ... if you really want to keep "ghost" centimeters !!!

Alain

[Ingvar]

Hi Tom,

What ranges are we talking about? Are you interested in altitudes higher than 21501 feet? If not, you can treat your input as a word(skip top 8 bits) and do your calculations on that. If you need to go higher, things will get more complicated but still possible. Higher than 65535 feet will get nasty ....

Do you really need 0.1m(0.3feet) resolution? Will 1m(3feet) enough?

Another thing .... you need to know how your inputdata(24bits) is formatted. My guess(based on your information) is that you are located at about 1096 feet. I'm assuming that "alt[3]" contains the most significant byte, 0,13,13 would be 000D0D in hex which is 3341 in decimal. 3341 tenths of a metre is 334.1m which is 334.1*3.28084=1096 feet.

/Ingvar

[Tom Gonser]

Thanks for the responses..

The precision is only tenths of meters. I don't know *why* the data is stored in 24 bits, it just is - not under my control, I am only trying to read it.

Regardless - the fundamental problem is that I have a 24 bit value stored in 3 bytes that I need to make into a variable I can do something with..... like read it digit by digit, and put a "." in the tenth's spot, and then multiply it by a factor to convert to feet..

TG