Mode 1 will return an array with the ASCII value as key and how many times it occurred as value (e.g. in this example, the ASCII value for the letter "l" is 108, and it occurs three times. The ASCII value for "space" is 32):

Array ( [32] => 1 [33] => 1 [72] => 1 [87] => 1 [100] => 1 [101] => 1 [108] => 3 [111] => 2 [114] => 1 )