Determining which flags are set from a hexadecimal input

Hi,

I'm currently looking into writing a program which reads a hexadecimal input, and then tells me which flags are set depending on what the hex input is.

For e.g. input - hex = 0062

output - 'Byte 0 bit 1 is set' therefore parameter x - 'Byte 1 bit 0 is set' therefore parameter y - 'Byte 1 bit 3 is set' therefore parameter z

Could anyone assist in what the best way would be to program this code?

Thanks

Answer 1

[Thorsten]

function flags = which_bit_set(hex_str)
x = dec2bin(hex2dec('hex_str'));

for i = 1:length(x)
  disp(['Bit ' int2str(i)])
    if x(length(x) - i + 1) == '0'
      disp(' not');
    end 
   disp('set')
end

[Darren]

Thanks Thorsten. How would you get this code to display a different word for each bit rather than every bit saying either set or not set?

i.e. bit 0 says either follow or not follow, bit 1 says either used or not used, bit 2 says ready or not ready etc?

[Walter Roberson]

parmname = {'set', 'used', 'ready', ...};

[...]
disp(parmname{i})

[Darren]

Where in the code to i enter those lines? I have tried the following:

function [ flags ] = which_bit_set(hex_str)
%UNTITLED3 Summary of this function goes here
%   Detailed explanation goes here
x = dec2bin(hex2dec(hex_str));    
for i = 0:7
disp(['Bit ' int2str(i)]) 
parmname = ['set', 'used', 'ready', 'past', 'help', 'seen', 'one', 'two'];
  if x(7 - i + 1) == '0'
    disp(parmname{i});
  end 
  disp('set')

end

However, this keeps producing errors!

[Walter Roberson]

function [ flags ] = which_bit_set(hex_str)
%UNTITLED3 Summary of this function goes here
%   Detailed explanation goes here

parmname = {'set', 'used', 'ready', 'past', 'help', 'seen', 'one', 'two'}; %curly brackets!!

x = dec2bin(hex2dec(hex_str));    
for i = 0:7
  disp(['Bit ' int2str(i)]) 
  if x(7 - i + 1) == '0'
    disp('not')
  end
  disp(parmname{i});
end

[Darren]

that code gives the following error:

Subscript indices must either be real positive integers or logicals.

Error in which_bit_set (line 13) disp(parmname{i});

[Walter Roberson]

disp(parmname{i+1});

[Darren]

Thanks Walter that error has fixed however the following error has occured:

Error in which_bit_set (line 4) parmname = {'set', 'used', 'ready', 'past', 'help', 'seen', 'one', 'two'}; %curly brackets!!

Output argument "flags" (and maybe others) not assigned during call to "C:\Documents\MATLAB\which_bit_set.m>which_bit_set".

[Walter Roberson]

Adapt:

    is_it_on = 'not ';
    flags{i+1} = ['Bit ', int2str(i), is_it_on, parmname{i+1}]);

Answer 2

[Jan]

Perhaps this helps:

Str = '0062';
Num = sscanf(Str, '%.2x');   % Or is it '%2x'? Or HEX2DEC()
for iByte = 1:2
  Byte = Num(iByte);
  for iBit = 0:7
    value = bitget(Byte, iBit);
    fprintf('Byte %d Bit %d: %d', iByte, iBit, value);
  end
end

This does not hit the "therefore parameter x" part, but I do not understand this expression.