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Translate between PETSCII and ASCII


PETSCII (PET Standard Code of Information Interchange), also known as CBM ASCII, is the character set used in Commodore Business Machines (CBM)'s 8-bit home computers, starting with the PET from 1977 and including the C16, C64, C116, C128, CBM-II, Plus/4, and VIC-20.

This library offers some support functions for translating between PETSCII and ASCII.


PETSCII has two different encodings (shifted and unshifted).

The shifted encoding includes both lowercase and uppercase letters and a small selection of block graphics. This was also called "text mode".

The unshifted encoding includes only uppercase letters but features a larger selection of block graphic characters and symbols, including things like symbols for card suits.


The following example shows how petscii could be used in a project:

var PETSCII, decode, encode;

({PETSCII} = require("petscii"));

({decode, encode} = PETSCII);

// "♠♥♣♦"
decode("unshifted", Buffer.from([0x61, 0x73, 0x78, 0x7a]));

// "ASXZ"
decode("shifted", Buffer.from([0x61, 0x73, 0x78, 0x7a]));

// Buffer.from([0x68, 0x45, 0x4c, 0x4c, 0x4f, 0x2c, 0x20, 0x57, 0x4f, 0x52, 0x4c, 0x44, 0x21])
encode("shifted", "Hello, world!");


The petscii module provides two functions decode and encode to translate between PETSCII and ASCII.

decode(mode, buffer) -> String

Translate a Buffer with PETSCII data to an ASCII String:

  • mode - One of 'shifted' or 'unshifted'
  • buffer - A Buffer object with data to be decoded

decode will return a UTF-8 encoded String

This function enforces types and may throw a TypeError if incorrect inputs are provided.

encode(mode, string) -> Buffer

Translate an ASCII String to a Buffer with PETSCII data:

  • mode - One of 'shifted' or 'unshifted'
  • string - A String containing data to be encoded

encode will return a Buffer with PETSCII encoded data

This function enforces types and may throw a TypeError if incorrect inputs are provided.

Unknown Characters

PETSCII does not include an encoding for all ASCII characters. For example, curly braces like { and } do not exist in PETSCII. Thus, there is no PETSCII code to represent them.

In the case of attempting to encode unknown characters, encode will replace them with a code of 0x3f (?) letting a question mark stand in as the character that could not be represented in PETSCII.

Note that one must be careful which mode one is using to encode. An ASCII string like Hello, world! can be encoded accurately in shifted mode. However, in unshifted mode, it will contain several question marks due to the lowercase letters that cannot be encoded.

// Buffer.from([0x48, 0x3f, 0x3f, 0x3f, 0x3f, 0x2c, 0x20, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x21])
encode("unshifted", "Hello, world!");

// H????, ?????!
decode("unshifted", Buffer.from([0x48, 0x3f, 0x3f, 0x3f, 0x3f, 0x2c, 0x20, 0x3f, 0x3f, 0x3f, 0x3f, 0x3f, 0x21]));


In order to make modifications to petscii, you'll need to establish a development environment:

git clone
cd petscii
npm install
node_modules/.bin/cake rebuild

The source files are located in src/main/coffee.
The test source files are located in src/test/coffee.

You can see a coverage report by invoking the coverage target:

node_modules/.bin/cake coverage


Copyright 2021 Patrick Meade.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see

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