Atari XL - Page 238

226
The Ateri XL Handbook
This is an 8-bit binary number, which represents
255 in decimal notation. To see how this is so, we
must first examine the decimal number and see
what it means.
HTU
255
means:
2*100 + 5*10 + 5*1
In other words, each digit is worth 10 times the one
to its right.
Binary notation uses this same 'place value'
principle, except each bit in a binary number is
worth double that to its right. We can assign
values to the eight bits in the same way as the
'h undreds, tens and uni ts' assigned to the digi ts of a
decimal number.
128 64 32 16 8421
11 111 111
By adding up, we can see why this number
represents 255:
1 *128
1 * 64
1 * 32
1 * 16
1 * 8
1 * 4
1
* 2
+1 * 1
255
You'll notice that 255 is the biggest number we can
represent with an 8-bit binary number. Hence this