􀂉 Adding the digits together from the
least significant digits
􀂾 If the result is less than 16, write that digit
as the sum for that position
􀂾 If it is greater than 16, subtract 16 from it
to get the digit and carry 1 to the next
digit
Ex. Perform hex addition: 23D9 + 94BE
23D9 LSD: 9 + 14 = 23 23 – 16 = 7 w/ carry
+ 94BE 1 + 13 + 11 = 25 25 – 16 = 9 w/ carry
B897 1 + 3 + 4 = 8
MSD: 2 + 9 = B

NUMBERING
AND CODING
SYSTEMS
Subtraction of
Hex Numbers
􀂉 If the second digit is greater than the
first, borrow 16 from the preceding
digit
Ex. Perform hex subtraction: 59F – 2B8
59F LSD: 15 – 8 = 7
– 2B8 9 + 16 – 11 = 14 = E16
2E7 5 – 1 – 2 = 2

NUMBERING
AND CODING
SYSTEMS
ASCII Code
􀂉 The ASCII (pronounced “ask-E”) code
assigns binary patterns for
􀂾 Numbers 0 to 9
􀂾 All the letters of English alphabet,
uppercase and lowercase
􀂾 Many control codes and punctuation
marks
􀂉 The ASCII system uses 7 bits to
represent each code
5A Z 7A z
59 Y 79 y
... ... ... …
44 D 64 d
43 C 63 c
42 B 62 b
41 A 61 a
Hex Symbol Hex Symbol
Selected ASCII codes

DIGITAL
PRIMER
Binary Logic
􀂉 Two voltage levels can be represented
as the two digits 0 and 1
􀂉 Signals in digital electronics have two
distinct voltage levels with built-in
tolerances for variations in the voltage
􀂉 A valid digital signal should be within
either of the two shaded areas
0
1
2        logic0
3
4     logic 1
5