Converting ASCII to HEX

[BobP]

Hi,

Can't think of how to do the following;

An 8 digit number in ASCII stored in 8 bytes need to be converted to a 4 byte hex number.
So 31724529 would become 01E413F1 stored as:
NUM1 = 01
NUM2 = E4
NUM3 = 13
NUM4 = F1

Have tried several methods but failed miserably! Any help, pointers or parts of code will stop me ripping my hair out (not much left now!).

Thanks,
BobP

[Jerson]

Not sure if I am suggesting the easiest way. Anyway, you can work it out. First convert the ASCII numbers to binary format in 4 bytes thus

31724529 = ((3*10) + (1*10) + (7*10) + ... + 9)

If this is what you want 01E413F1, 'you got it'

If you want to send this as hex digits, you need to pick one number at a time and send the nibbles. For example, E4 will be sent as 'E' and '4'. To do this, you split the E4 into 0E and 04. To make any number to printable hex, you need to check; if it is in 0..9, simply add 30H and you got the printable hex. However, if the number is between 0A to 0Fh, you add 37H to get the printable Hex digit.

Hope this sets you on the right track.

Jerson

[ErnieM]

Interesting problem. You’ve just maxed out the capabilities of PIC basic, which is most happy with 16 bit numbers, but has some facilities to get out 32 bits.

The basic algorithm is simple: Start from the most significant ASCII digit, convert to binary, add the binary to a sum. If more digits, multiply the sum by 10 and repeat for the next digit. Actually, when you implement this you zero out the sum first, then do the times 10 multiply at the top of the loop (saves you the code for checking for the last run of the loop).

Converting ASCII to binary is simple: just subtract $30 (ASCII zero) from the ASCII and you got it!

In the code below we use temp for the binary, and BottomSum and TopSum for the sum. We need 2 words for the sum to get 32 bits. The next trick is to recognize that PBP has 2 different multiplication methods, * and **. When you multiply two 16 bit numbers the result can be as high as 32 bits. PBP handles this by using * to return the lowest 16 bits and ** to return the highest 16 bits. We use both methods to accumulate a 32 bit sum for the times 10 part.

The following code will compile, but has not been properly debugged. Always code defensively when using integer arithmetic where an overflow can give you buggy results.

    ASCII var BYTE[8]           ' holds the 8 orgional ASCII digits
    HexResult var byte[4]       ' place for 8 hex digits (4 bytes)
    BottomSum var Word          ' BottomSum & TopSum used to store 16
    TopSum var word             '  bit results
    LastBottom var byte         ' result of last operation to BottomSum
                                '  used to detect overflows
    Index var byte              ' pointer
    temp var word               ' tempory intermediate result
    
    ' fill ASCII with data  ASCII[]= 31724529
    ASCII[0]= 9
    ASCII[1]= 2
    ASCII[2]= 5
    ASCII[3]= 4
    ASCII[4]= 2
    ASCII[5]= 7
    ASCII[6]= 1
    ASCII[7]= 3

    BottomSum =0
    TopSum =0
    LastBottom = 0
    For Index = 7 to 0 step -1
        ' first, take total accumlated in the sums and multiply by 10
        TopSum = TopSum * 10                ' direct multiply
        BottomSum = BottomSum * 10          ' also a direct multiply
        TopSum = TopSum + BottomSum ** 10   ' top 16 bits of the multiply 
        ' convert ascii to number,add to accumulated sum
        temp = ASCII[Index] - $30   ' convert ascii digit to binary
        bottomSum = BottomSum + temp
        ' check bottom result in case of overflow, if so, bump top result
        ' ( an overflow will give a result smaller then the existing value)
        if bottomSum < Lastbottom then TopSum = TopSum + 1 
        LastBottom = bottomSum                  ' set for next iteration
    next index    
    
    ' now we have the result in Top & Bottom Sum, move to HexResult array
    HexResult[0] = bottomsum.byte0
    HexResult[1] = bottomsum.byte1
    HexResult[2] = Topsum.byte0
    HexResult[3] = Topsum.byte1

[BobP]

Many thanks for all the replies.

Was going down the same route but my code wasn't as neat.

Will try the code later this week.

Many thanks again,
BobP