Bit: The smallest unit in computers. It is either a 1 or a 0.
Nibble: Half a byte, or 4 bites.
Byte: 8 bits together form one byte, a number from 0 to 255. Bits in the byte are numbered starting from the right at 0.
Short: Two bytes put together is 16 bits, forming a number from 0 to 65535. The low byte is the rightmost eight bits.
Hex Number: A HEX number consisting of 4 numbers is 16-bit.
Hexadecimal to Binary Conversion
0
0000
4
0100
8
1000
C
1100
1
0001
5
0101
9
1001
D
1101
2
0010
6
0110
A
1010
E
1110
3
0011
7
0111
B
1011
F
1111
Arithmetic
Addition
input
ADD
output
carry
0
1
1
0
0
0
0
0
1
1
0
1
1
0
1
0
Subtraction
input
SUB
output
borrow
0
1
1
1
0
0
0
0
1
1
0
0
1
0
1
0
Multiplication
input
MUL
output
0
1
0
0
0
0
1
1
1
1
0
0
Bit Masks
AND, or "both", sets individual bits to 0. AND is useful for masking bits, for example, to mask the high order bits of a value AND with $0F: $36 AND $0F = $06.
input
AND
output
0
1
1
0
0
0
1
1
0
1
0
1
ORA(OR), or "either one or both", sets individual bits to 1. OR is useful for setting a particular bit, for example, $80 OR $08 = $88
input
ORA
output
0
1
1
0
0
0
1
1
1
1
0
1
EOR(XOR), or "one or the other but not both", inverts individual bits.
input
EOR
output
0
1
1
0
0
0
1
1
0
1
0
1
Signed Integers
If Bit 7 is not set (as in the first example) the representation of signed and unsigned numbers is the same. However, when Bit 7 is set, the number is always negative. For this reason Bit 7 is sometimes called the sign bit.
