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Read-Only Author
Adi Sapner Posted
11-Dec-2004 18:28 GMT Toolset
C51 |  Need BINARY to BCD function Adi Sapner Hi,
Does anyone know how to convert a BINARY 8 bit to a 2 digit packed BCD.
Example if I have value 0x0C (wich is 12 decimal) the result will be 12 or a char value of 0x12.
thank you,
Adi, |
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Read-Only Author
Graham Cole Posted
13-Dec-2004 09:09 GMT Toolset
C51 | RE: Need BINARY to BCD function Graham Cole This wouldn't be homework would it?
Firstly, an 8-bit value will be in the range 0 to 255, so obviously some values require more than 2 decimal digits.
To convert a value in the range 0..99, simply divide the value by 10 to obtain the most significant digit and take the modulo 10 value to obtain the least significant digit. The DIV instruction will all this in one go.
Compacting two digits into one byte requires moving some bits and ORing the results together.
To convert a decimal digit to ASCII, you just have to add a magic value. |
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Read-Only Author
Adi Sapner Posted
13-Dec-2004 14:20 GMT Toolset
C51 | RE: Need BINARY to BCD function Adi Sapner Hi,
Thanks for the HELP. No its not homework...I finished school long time ago :-) It was for communicating with a DALLAS RTC DS1337.
Is your code better than this one ? I mean will it run faster ?
Because I didn't use the MODULO 10, here is what I did:
char bin2BCD8(char cValue)
{
char cDig10=0;
char cDig1=0;
char cTemp;
cTemp=cValue; // Backup the value
do{
cTemp=cTemp-10;
if(cTemp<0)
{
break;
}
else
{
cDig10++;
}
}while(1);
cDig1=cValue-(cDig10*10);
cDig10=(cDig10<<4)|cDig1;
return cDig10;
} |
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Read-Only Author
Ingvar Kreft Posted
13-Dec-2004 14:30 GMT Toolset
C51 | RE: Need BINARY to BCD function Ingvar Kreft Hi
unsigned char chartobcd(unsigned char n)
{
return ((n / 10) << 4) | (n % 10);
}
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Read-Only Author
erik malund Posted
13-Dec-2004 14:37 GMT Toolset
C51 | danger af assumptions erik malund the above should be
unsigned char chartobcd(unsigned char )
{
if (n >99) crash();
return ((n / 10) << 4) | (n % 10);
}
While the code, indeed, works, any function that can not handle all values of the input (255 for a byte, ffff for an int) should trap invalid input values. Bugs occuring from someone seeing the above function prototyped and use it can be lenghty to trap.
Erik |
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Read-Only Author
Adi Sapner Posted
13-Dec-2004 14:50 GMT Toolset
C51 | RE: danger af assumptions Adi Sapner Hi,
WOW I'm learning from the PRO...your code seems very compact.
I will try it. But will I get a packed BCD value ?
I'll get back to you if I have some problems.
Thank you,
Adi, |
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Read-Only Author
Stewart J Cort Posted
13-Dec-2004 15:10 GMT Toolset
C51 | RE: danger af assumptions Stewart J Cort will I get a packed BCD value ?
Yes, by "ORing" the two halves of the number together, you get a single byte, two digit BCD number. |
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Read-Only Author
Hans-Bernhard Broeker Posted
13-Dec-2004 16:15 GMT Toolset
C51 | RE: danger af assumptions Hans-Bernhard Broeker And now the add-on question for extra points: how many assembly instructions is the minimum this functionality can be achieved in? You may assume all inputs are already in the correct registers, and it doesn't matter where the output is, as long as it's somewhere. |
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Read-Only Author
J. Lehmo Posted
15-Dec-2004 10:41 GMT Toolset
C51 | RE: danger af assumptions J. Lehmo But what is the more interesting value - the number of assembly instructions or code efficiency? A DIV and MODULO takes very long, so it might be better to use some add-and-compare loops
Jochen |
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Read-Only Author
Hans-Bernhard Broeker Posted
15-Dec-2004 13:34 GMT Toolset
C51 | RE: danger af assumptions Hans-Bernhard Broeker A DIV and MODULO takes very long,
Indeed. And it's too many instructions, anyway ;-) So sorry, but no cigar yet. |
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Read-Only Author
Ingvar Kreft Posted
13-Dec-2004 14:58 GMT Toolset
C51 | RE: danger af assumptions Ingvar Kreft Hi
If a want to write a BCD number to a RTC, I prefear to do that check in the input routine, and that because of the different of input values.
year = 00 - 99
month = 01 - 12
day = 01 - 31
hour = 0 - 23
min = 0 - 59
sec = 0 - 59
Ingvar |
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Read-Only Author
Brad Holeman Posted
15-Dec-2004 15:38 GMT Toolset
C51 | RE: danger af assumptions Brad Holeman if (n >99) crash();
The above line (or something akin to it) is used thousands of times in all Microsoft products. They of course document better so their equivalent would be.
/* Randomly screw the customer so they purchase an upgrade. *.
if (user_is_doing_something_important)
{
crash_horribly_and_do_not_save();
}
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