echo $(printf %08X 256 | grep -o .. | tac | tr -d '\n')
example of 256
printf %08X
produces the 8 characters 00000100
grep
breaks string by two characters
tac
reverses
tr
00010000
could be put in a loop like this
for A in $(printf %08X'\n' 256 255); do echo $A | grep -o .. | tac | tr -d '\n'; done