$ perl -e 'print"unsigned   signed\n";printf"%-3d %08b %4d\n",$_,$_,unpack"c",pack"C",$_ for 0..255'
unsigned   signed
0   00000000    0
1   00000001    1
2   00000010    2
3   00000011    3
...
125 01111101  125
126 01111110  126
127 01111111  127
128 10000000 -128
129 10000001 -127
130 10000010 -126
...
253 11111101   -3
254 11111110   -2
255 11111111   -1