A problem with PIC16F876 and some function

[diego101]

A problem with PIC16F876

I have to realize the function

(X-18000)*(4095/22000)

with a PIC16F876.
X is in the range 18000-40000.
Anyone can help me please!?Thanks!!!!!!

 

[C-Man]

Which language are you planing to use?

In C this is easy if you do not have a problem with codesize ...

In assembler this will not be sooo easy.

In Assembler you could work like this:
shift your two bytes number (that you want to multiply by 4095) 4 bits to the left (which is a multiplication by 16) now you have a three bytes result. Now add a fourth byte 0x00 byte to your three bytes (you would have to shift your number 8 bits to the left which can be eliminated by just adding another 0x00 byte to the end of your result) which gives you a 4 bytes result (your original number multuplied by 4096) next subtract your original number, now you have an intermediate result (your original number multiplied by 4095).

Afterwards use this:
http://www.piclist.com/techref/microchip/math/div/div16or32by16to16.htm

to do the division by 22000

hope this helps

 

[diego101]

FOR C-MAN

I'm using ASSEMBLER!
To program the PIC16F876 i can use only the ASSEMBLER!!
Could you help me!?It's very important!!
Thank you!!

 

[neuralc]

Use a C compiler to build your assembler code !

NeuralC

 

[C-Man]

I did not want to suggest this because the assembler code which is generated for example by Hi-Tech C is in no way compatible with Mplab.

Also if you use high optimization (in Hi-Tech) the code is very hard to understand and integrate into another application ...

But it could be a point to start

best regards

 

[volta]

An Easy Solution

Use the the document for the implementation of the following FIXED POINT routines:

- Addition
- Subtraction
- Multiplication
- Division