How to convert 0xffff to -1?

I'm controlling a DAC with Matlab. I want to display the voltage that I'm setting the DAC to. The DAC voltage range is from -10 to 10v and the DAC treats the input value as a signed integer. If I cast 0xffff into int16 Matlab gives me maxint (32767) or if I cast into int32 I get 65535.

For example:

DACsetting = hex2dec('ffff')

%Display the setting

fprintf('%d\n', DACsetting * 10/(2^15 -1));

I can write buch of extra code to work around this, but this should be a very simple thing for a language to do.

DACsetting = hex2dec('ffff')

DACsetting =

65535

>> fprintf('%d\n', DACsetting * 10/(2^15-1))

2.000031e+01

fprintf('%d\n', int16(DACsetting) * 10/(2^15-1))

1

Thanks in advance.

Answer 1

[Walter Roberson]

typecast(uint16(hex2dec('ffff')), 'int16')

[Stephen Galperin]

I want to use the contents of the variable DACSetting as the source rather than the string 'ffff'. DACSetting will be an array of values the DAC will be set to.

[James Tursa]

So, instead of using 'ffff' use DACSetting. Is DACSetting a char array, a cell array, or ...?

[Walter Roberson]

DACtext = 'ffff';
DACSetting = 10 * (double(typecast(uint16(hex2dec(DACtext)), 'int16')) / 32768);

[Stephen Galperin]

Thank you all. It looks like I'm going to have to store the DAC commands as a char array and convert when I need them. This was my work around but I had hoped their was some way to make Matlab convert 0xffff to -1. It looks like there isn't.

Thank you once again.

[Walter Roberson]

? You showed your input as character vector so that is what I programmed.

MATLAB has no direct 0xffff only '0xffff' or 'ffff' or binary values equivalent to 65535 integer, or double precision representation of 65535. What is your actual input?