 |
 |
| View previous topic :: View next topic |
| Author |
Message |
lgeorge123
Joined: 05 Dec 2004
Posts: 31
|
| multiplication a floating point number to a hex number |
 Posted: Wed Dec 07, 2005 1:32 am |
 |
|
I need help of using pic16f877 to multiply hex number e.g. 0x34 to a
floating point number like 61x10-6(0.000061) and display the result to
two to three variables,each are 8 bits,anyone knows the c source ?????? |
|
 |
Ttelmah
Guest
|
|
| Posted: Wed Dec 07, 2005 3:21 am |
|
|
I think you need to understand numbers. Inside a computer, there is no such thing as either a fp number, or a hex number. Everything is binary. Hex, is just a way of 'representing' these values, and fp, is another (more complex) way of using these values to cover a wider 'range' of values.
Now if you code:
| Code: |
int8 x=0x34;
float y=6.1E-5;
float z;
z=y*(float)x;
|
'z', will now be the fp representation of 0.003172. In 'hex', it should be 0x764FE154. If you wanted 3 hex digits (003), then use sprintf, to output it as:
| Code: |
char out[5];
sprintf(out,"%03lx",(int16)(z*1000.0));
|
Which will place the digits '0', '0', '3', into the array 'out'. The digits beng placed are 'hex', in that if you had a result that was 0.011, the output would be 00B.
Now the point is that 'hex', is just a way of representing binary values. You could output the fp value in hex (will give 8 characters as shown above), or convert just part of the number, back to integr, and output this to hex 'text' output values (as shown using the printf), or just output the bytes themselves (four 8 bit characters). All can be represented in 'hex'. You need to work out what format you actually want the data in, then rephrase the question.
Best Wishes |
|
|
lgeorge123
Joined: 05 Dec 2004
Posts: 31
|
| multiplication a floating point number to a hex number |
| Posted: Thu Dec 08, 2005 8:51 pm |
|
|
Hi Ttelmah, actually I wish to use ADC to measure analog current across
a 1 ohm resistor and display the data to LCD. Suppose 0.61A drops in
1 ohm resistor would produce 0.61V, according to ADC datasheet, 0.61V result in 0x27 in highbyte and 0x10 in low byte or 0x2710. Every 61x10-6
(0.000061v) output a 1bit, 0x2710 means 0x2710*0.000061 or 0.61V,so I knows that 0.61A has been measured, but the problem is how to multiply
two numbers and 'generate' a meaningful output , just like '0', '.' , '6',
'1' , could someone or you help me ???????? |
|
|
ttelmah
Guest
|
|
| Posted: Fri Dec 09, 2005 5:13 am |
|
|
Read your two bytes into an int16 (use make16, to put the result into a single 16bit integer value). You now have a value of '10000' in this integer (0x2710, is just a way of representing this). Your conversion factor, is then 0.000061. So:
| Code: |
//In 'psuedo code'
float voltage;
int16 val;
//Read your adc value into 'val' here
val=get_adc_reading();
voltage=val*0.00061;
//Now voltage contains the fp representation of 0.610
//What you do now, depends on what you want.
//So, to display this:
printf("%5.3g",voltage)
//This will output 0.610 - adjust format as needed
//The 'justification', is faulty on older compilers, and the latest
//few versions have developed fp bugs, so you want something
//like 3.236
|
Best Wishes |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
FAQ 
Search
Register
Profile 
Log in to check your private messages 
Log in
