Character Encoding¶
Commodore systems used a 8-bit character encoding commonly referred to as PETSCII. Modern computer systems use a variable length encoding called Unicode. In order to translate between these formats a set of encoding and decoding tables known as codecs are used.
Multiple codecs exist because there are multiple variants of PETSCII which differ slightly between different models. In addition most systems have two separate character sets
upper case letters and graphics characters
lower case and upper case letters
When displaying the contents of directories and BASIC strings the current codec is used to produce the correct representation. It is also used for converting file names entered by the user.
The current codec is stored in the encoding setting:
(cbm) set encoding
encoding: 'petscii-c64en-uc'
The middle part is a combination of the system name followed by the
language. The final part of the encoding name indicates the case, to
switch to a codec with lower case characters set a new value ending
lc:
(cbm) set encoding petscii-c64en-lc
encoding - was: 'petscii-c64en-uc'
now: 'petscii-c64en-lc'
Control Characters¶
PETSCII contains many non-printing control characters which cause
effects such as a change of foreground colour, reverse video
etc. These are usually displayed as a reverse video character, for
example a reverse video S represents the cursor home character.
These representations are not easy to enter in Unicode and are
therefore replaced by a string enclosed in curly brackets, for example
the cursor home character is shown as {home}.
The mapping of these sequences is achieved by a separate table derived from the current codec.
Converting Strings¶
Text strings can be converted from Unicode to the current
representation of PETSCII using the to_petscii command:
(cbm) to_petscii "2↑3"
b'2^3'
Conversion from PETSCII to Unicode can be done using the
from_petscii command, non-printable characters can be escaped
using the usual Python syntax:
(cbm) from_petscii b'\xab\x60\xb3'
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