Instruction Set Reference - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 787

B.14 Representing Nonnumeric Data

Computers are also used to process nonnumeric data. Nonnumeric data is often in the form
of character strings. A character can be a letter, a digit, or a special character symbol. A unique
number is assigned to each character of the character set so that it can be differentiated by the
computer. To facilitate the processing of characters by the computer and the exchange of infor-
mation, all users must use the same number to represent (or encode) each character.
Two character code sets are in widespread use today: ASCII (American Standard Code for
Information Interchange) and EBCDIC (Extended Binary Coded Decimal Interchange Code).
Several types of mainframe computers use EBCDIC for internal storage and processing of char-
acters. In EBCDIC, each character is represented by a unique 8-bit number, and a total of 256
different characters can be represented. Most microcomputer and minicomputer systems use
the ASCII character set. A computer does not depend on any particular set, but most I/O devices
that display characters require the use of ASCII codes.
ASCII characters have a 7-bit code. They are usually stored in a fixed-length 8-bit number.
The 2 7 5 128 different codes are partitioned into 95 printable characters and 33 control charac-
ters. The control characters define communication protocols and special operations on peripheral
devices. The printable characters consist of

26 uppercase letters (A-Z)

26 lowercase letters (a-z)

10 digits (0-9)

1 blank space

32 special-character symbols, including

! @ # $ % ^ & * () 2 _ 5 1 ' [] ; : '” , , . . / ? {}

The complete ASCII code set is shown in Table B.2.