changing hex value to decimal

The problem with the above code is that we don't know if the OP know what BCD is. Was 0x15 -> 15 attempted to be a BCD to decimal conversion or an accidental evaluation error?

We constanly suffer from people that don't want to describe what problem they have. They first want to make a couple of own assumptions and then asks a half-mashed question that can't be answered because of lack of information, and often shouldn't even be answered since it is based on the OP being half-way down the wrong path.

If BCD was intended, then the next thing is if there is a need for error recovery - is there a chance that the above function may be called with an invalid BCD value that must be correctly detected? 0xff -> 165 wouldn't be so fun, but isn't a problem if there is screening of the values earlier in the process.

We constanly suffer from people that don't want to describe what problem they have.

I think suffering is the wrong word. To me it's fun :-)

First sorry if i irritated you all.

I know how to convert hex "0x15" to decimal 21.

I am using a RTC DS1307 with 89s52 and displaying time in LCD.

have to write and read in hex only with the RTC.

I can write and read the values in RTC and also displayed it in LCD.

The problem for me is when i try to edit the time.

I receiving it in hex and if i directly send it to LCD and edit, the value after 09 became some other characters. if i convert it to decimal and send to LCD it works.

But in the first place itself, if i read 0x15 it displays 21 because i converting it to decimal.

That's why i need to change the hex '0x15' to decimal 15 not 21.

I think you may understand my problem. if not again sorry.

i thought keil will have some option for this, like the typecast.

Thankyou

In other words, you are using BCD or Binary-Coded Decimal - or, strictly, packed BCD.

In packed BCD, each nibble of the binary data holds one digit of the decimal value.

So, all you need to do is to extract the individual nibble values, and display them as the digit values.

You can extract the individual nibble values by using the standard 'C' shift & mask bitwise operators.

This really is a very common task indeed - you should easily be able to find plenty of examples...

Thank you for the all

Thank you Mike Kleshov, i solved my problem from your reply.

Regards
arun

Mike's post shows how to convert BCD to a numeric value.

If you just need to display the value, there isn't really any point in converting to a number - you could just extract the digits and then display them directly.

"have to write and read in hex only with the RTC."

Not at all. Hexadecimal is a presentation of a number. Something you may have in your source code. Or dispayed on the LCD. Or printed on a paper. But you do not program the RTC with any hexadecimal data, for the simple reason that the RTC want to see bytes without caring about the existence of any radix or numeric base you may have in your source code.

In this specific case, it's BCD-encoded data. When printing to display, you can use %02x to print it, giving a correct 2-digit presentation of the BCD-encoded value. Or you can use the previous source code to convert into a number and print it using %02u.

If you implement code to edit/input the time, then you can select if your code should use a number 0..59 for minutes and convert to BCD just before sending to the RTC. Or if the code should directly have a BCD value in a byte and (if you have up and down buttons) code that knows that 0x09 + 1 should be 0x10, i.e. that when low nibble increments from 9 it has to be reset to 0 while the high nibble must be incremented. And similar when low nibble is decremented while already being 0.