The character set
Two hundred and fifty-six characters, in ROM, eight bytes each. They are IBM Code Page 437 — the set the original PC shipped with, which is why it has box-drawing lines, card suits, Greek letters and three densities of shading alongside the alphabet.
Each glyph is an 8 × 8 cell with the drawing five pixels wide and pushed to the left of the byte. The Kernal copies the whole lot into the video card at power-on, so this table is what the screen has to work with.
Row is the high hex digit, column the low one. A is row 4, column 1 — $41, which is also 65, which is also what ASC("A") tells you.
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0x | ||||||||||||||||
| 1x | ||||||||||||||||
| 2x | ||||||||||||||||
| 3x | ||||||||||||||||
| 4x | ||||||||||||||||
| 5x | ||||||||||||||||
| 6x | ||||||||||||||||
| 7x | ||||||||||||||||
| 8x | ||||||||||||||||
| 9x | ||||||||||||||||
| Ax | ||||||||||||||||
| Bx | ||||||||||||||||
| Cx | ||||||||||||||||
| Dx | ||||||||||||||||
| Ex | ||||||||||||||||
| Fx |
What PRINT can reach
Not all of it — and this is the thing that catches people.
PRINT CHR$(n) goes through the Kernal's Chrout, and Chrout's video path passes $20 to $7E through to the screen, honours four control codes (carriage return, line feed, backspace and bell), and discards everything else. That includes every code from $7F up: all the box drawing, all the shading, every accented letter.
So this does nothing at all:
PRINT CHR$(219)The character is there in ROM. It is Chrout that will not pass it on.
Getting at the rest
From assembly there is a second routine, VideoChroutRaw, which puts any of the 256 codes on the screen unfiltered. That is how a program draws a box or fills an area with shading — see The screen.
From BASIC, the way to reach the upper half is to redefine the characters you can print. The pattern table is writable, so you can point A at whatever shape you like and then print A.
Which codes are which
| Range | What is in it |
|---|---|
$00–$1F | Faces, card suits, arrows, musical notes. Historically the control codes; here they are pictures |
$20–$7E | Space, punctuation, digits, capitals, lower case — plain ASCII, and the only part PRINT will pass |
$7F | A house |
$80–$AF | Accented letters, currency, fractions, Spanish punctuation |
$B0–$B2 | Light, medium and dark shading — the three densities |
$B3–$DA | Box drawing, single and double lined |
$DB–$DF | Solid blocks: full, half, quarters |
$E0–$FE | Greek letters and math symbols |
$FF | A blank, distinct from space only in that it is a different code |
Where it lives
The set sits at $B800–$BFFF, immediately above the Kernal and below BASIC. It is 2 KB of the 32 KB ROM: 256 characters × 8 bytes each, exactly.
The memory map has the rest of the ROM; The screen covers writing to the pattern table and the character-set tricks that make text-mode games work.
📄 Character Set card — the whole grid plus every glyph's name, on three printable pages.