The DOS unit implements the following constants:
{Bitmasks for CPU Flags}
fcarry = $0001;
fparity = $0004;
fauxiliary = $0010;
fzero = $0040;
fsign = $0080;
foverflow = $0800;
{Bitmasks for file attribute}
readonly = $01;
hidden = $02;
sysfile = $04;
volumeid = $08;
directory = $10;
archive = $20;
anyfile = $3F;
fmclosed = $D7B0;
fminput = $D7B1;
fmoutput = $D7B2;
fminout = $D7B3;