Interpreting character array as hex data

Hi

I want to write a MAC address to a flash device. The address is generated by matlab and is in hex format, but strored as a character array (see code). When I write the variable to a binary file, matlab converts the characters to binary which is not what I want as my data already is hex formated.

macAddr = '0050c246d880';

fid = fopen('macAddr.bin','w');
fwrite(fid, macAddr);
fclose(fid);

% file content:  "30 30 35 30 63 32 34 36 64 38 38 30" (hex interpreted)

I solved this problem by splitting the address into bytes and converting them to decimal:

macAddr = '0050c246d880';

% Split address to bytes and store them as decimal numbers
macAddrDec = '';
for i=1:length(macAddr)/2
    macAddrDec(i) = hex2dec(macAddr(i*2-1:i*2));
end

fid = fopen('macAddr.bin','w');
fwrite(fid, macAddrDec);
fclose(fid);

% file content:  "00 50 c2 46 d8 80" (hex interpreted)

This works, but isn't there an easy way to tell matlab that a character array is already hex formatted?

Cheers Simon

Answer 1

[Walter Roberson]

You are mistaken in your interpretation that the data is being stored in hex in the file. The data is stored in binary and some program you are using is showing you the hex equivalent of the binary.

The character string is in the character representation of hex, not hex itself, and needs to be interpreted as binary in order to write it, using logic such as you have come up with.

[Simon]

Yes of course, you are right, I always forget that TextPad shows me the hex interpretation of binary files. I would still have hoped that there would have been a smarter way to achive my goal.

[Walter Roberson]

fwrite(fid, sscanf(macAddr, '%2x'));

which is merely a more compact way and not a smarter way.

Answer 2

[Jan]

You can write the data in CHAR format:

macAddr = '0050c246d880';
fid = fopen('macAddr.bin','w');
fwrite(fid, macAddr, 'char');
fclose(fid);

Walter suggested sscanf for the conversion from HEX to DEC already: This is much faster than hex2dec.

[Simon]

What output do you get with this? I get the same as without this option and that is not what I want.