AUTHOR'S PREFACE



So $F equals 15 in decimal. Now here's how it all relates to binary math
and bits:

Each byte can be broken up into two parts (nybbles), like this:
0000	0000

If each nybble is considered a separate number, in decimal, the value
of each would range from zero to 15, or zero to $F. Aha! So if all the
bits in each group are on (one, or set), then you have:
1111  1111  Binary
  15    15  Decimal
   F     F  Hex

You join the two hex numbers together and you get SFF (255 in deci-
mal), the largest number a byte can hold. So you can see how we
translate bytes from binary to hex, by translating each nybble. For
example:
1001  1101  Binary
   9    13  Decimal
   9     D  Hex

$9D equals nine times 16 plus 13, or 157 in decimal.
0100  0110  Binary
   4     6  Decimal
   4     6  Hex

$46 equals four times 16 plus six, or 70 in decimal.
1111  1010  Binary
  15    10  Decimal
   F     A  Hex

$FA equals 15 times 16 plus ten, or 250 in decimal.
Obviously, it is easier to do this with a translation program or a
calculator!

Since I will often be discussing setting bits and explaining a small
amount of bit architecture, you should be aware of the simple
procedures by which you can turn on and off specific bits in any
location (that is, how to manipulate one of the eight individual bits
within a byte). Each byte is a collection of eight bits: numbers are
represented by turning on the particular bits that add up to the number
stored in that byte. Bits can be either zero (0 equals off) or one (1
equals on, or SET). The bits are numbered zero to seven and represent
the following decimal numbers:
Bit      7   6   5   4   3   2   1   0
Value  128  64  32  16   8   4   2   1

The relationship between the bits and the powers of two should be