The Commodore 64 uses two related but different values to display text: PETSCII for characters and control actions handled by BASIC and the KERNAL, and screen codes stored in screen memory to select glyphs for the VIC-II. The glyph itself is an 8-by-8 pattern, while its color is stored separately. Keeping those three things—input encoding, glyph selection, and color—distinct explains why a byte that prints “A” is not the same byte you write directly to screen RAM.
How does the Commodore 64 character set work?
When the VIC-II displays a character in standard character mode, it reads a screen code from screen memory and uses that code to find the glyph pattern in character memory. The character’s color comes separately from color memory. A screen position therefore does not store a complete letter or its color in one value: character selection and color are separate.
Each built-in glyph is an 8-by-8 grid represented by eight bytes, one byte for each row. Within a row, the bits specify which dots are on. The Commodore 64 Programmer’s Reference Guide describes it this way: “Each character is formed in an 8 by 8 grid of dots, where each dot may be either on or off.” Commodore 64 Programmer’s Reference Guide, “Character Definitions”.
The VIC-II can use character patterns in character-generator ROM for the standard set, or be configured to read character data from RAM. RAM makes custom glyphs possible: a program can draw its own eight-row patterns and direct the video chip to use them. Because the custom data takes the place of the standard set for that configuration, a program that still needs ordinary letters or symbols must copy those patterns into its custom character set too. The guide explains the display and programmable-character arrangement in “Standard Character Mode”.
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What is the difference between PETSCII and screen codes?
PETSCII is the character and control-code system used by the C64’s KERNAL and BASIC interfaces. BASIC statements such as PRINT, CHR$(), GET, and INPUT work with PETSCII, as do keyboard and file operations. A PETSCII value may represent a visible character, but it may instead tell the screen editor to change color, move the cursor, toggle reverse video, or switch character-set mode. It is not safe to treat every byte as printable text.
Screen codes are different: they are the values written into screen RAM to choose which glyph the VIC-II displays. For example, uppercase A is PETSCII 65, but its screen code is 1 in the uppercase/graphics set. Digits, spaces, and some punctuation share values between schemes, which can conceal the distinction until a program handles letters or graphic symbols. The mapping and control-code distinction are laid out in Appendix G — PETSCII, Screen Codes & Color Codes.
Reverse video illustrates why the route matters. With BASIC output, reverse video is a PETSCII state controlled through the character stream. With direct screen-memory placement, the corresponding reversed glyph is represented by a screen code in the reverse range. In either case, color remains a separate value rather than being encoded as part of the character glyph.
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How do I get PETSCII graphics on a C64?
Print a character through BASIC
For BASIC PRINT, provide PETSCII. CHR$(n) constructs a byte value, which may print a symbol or perform a control action, depending on the code and current display state. The exact visible result can depend on which built-in character set is active; a control code that selects a mode changes the active glyph set, not the underlying meaning of screen RAM values.
Place a glyph directly in screen memory
For direct writes to screen RAM, use screen codes for the active character set rather than assuming a PETSCII value will select the same glyph. In uppercase/graphics mode, for example, write screen code 1 to display uppercase A. Set the desired color independently in color memory. This method is useful when a program needs precise control over screen positions without sending characters through BASIC’s screen editor.
Make custom graphics
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Prepare the character patterns in RAM. Each glyph needs eight bytes, one for each of its eight rows; set the bits for the dots that should appear.
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Configure the VIC-II to use the RAM character data for the display. Character-pattern addresses depend on the selected screen code, character-set location, and VIC-II memory bank; the Programmer’s Reference Guide gives the relationship as
CHARACTER ADDRESS = SCREEN CODE*8 + (CHARACTER SET*2048) + (BANK*16384). -
Copy any standard glyphs your program still requires into the RAM character set, since custom character data replaces the standard set in that configuration.
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Write the appropriate screen codes into screen RAM and set colors separately in color memory.
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What are the C64’s two built-in character sets?
The C64’s built-in sets trade access to lowercase letters against access to graphic symbols. Switching sets changes which glyph pattern a code displays; it does not make PETSCII and screen codes interchangeable.
| Set | Letters available | Graphics | How selection works |
|---|---|---|---|
| Uppercase/graphics | Uppercase letters | Includes graphic and block symbols useful for text-mode pictures, borders, and interfaces. | Selected through system or video configuration; BASIC control codes are also commonly used to select a mode. |
| Lowercase/uppercase | Lowercase and uppercase letters | Fewer graphic symbols than the uppercase/graphics set. | Selected through system or video configuration; BASIC control codes are also commonly used to select a mode. |
The visible choice is practical: use uppercase/graphics when a text screen needs its broader set of built-in symbols, or the lowercase/uppercase set when both letter cases matter more. For a custom set, the same principle applies at a lower level: the VIC-II displays the glyph patterns the configured character memory provides.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Keep the three display values straight
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PETSCII: the character and control-code values used by BASIC, the KERNAL, keyboard input, and file operations.
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Screen code: the value in screen RAM that selects a glyph for the VIC-II.
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Color: a separate value in color memory or the relevant video registers; it does not select the glyph.
For a deeper technical treatment, the Commodore Programmer’s Reference Guide chapter on graphics covers standard character mode and programmable character shapes: Standard Character Mode and Character Definitions.
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