The C64 Dead Test Font
The C64 Dead Test Font
May 24, 2026<br>A deep dive into the font of the “Dead Test” diagnostic cartridge of the C64, including an Easter egg, a look into the implementation, and, finally, some Commodore 8-bit character ROMs for download.
Recently, having a cursory look around at the Web, this yielded an alarming result: there’s apparently no documentation of the iconic font of the C64 Dead Test cartridge, no character chart, no read-out, nothing of note. A scandalous omission, we’re attempting to remedy here.<br>(The same font is also implemented in the more advanced Rev. 586200 diagnostic cartridge, Commodore part № 326070-01, the one using a test harness, and the similar Rev. 588220 for the SX64.)
The Cartridge Font
The C64 “Dead Test” diagnostic cartridge Rev. 718220 (Commodore part № 314139-03) famously comes with a special font, embedded in its ROM, thus not using the built-in Character ROM of the C64, in fact requiring none of the built-in ROMs to be working (hence the name), as it comes all in stand-alone package. (We’ll see later how it does this.) Its display font is somewhat special and is, to my knowledge, not used anywhere else and, maybe for this very fact, instantly recognizable to anyone who has ever seen it.
And this is what the display of the “Dead Test” cartridge looks like:
Screenshot of the C64 Dead Test diagnostic cartridge in action.<br>Source: zimmers.net (processed for CRT-like appearance; N.L.)
Jus as a reminder, here’s the normal font used by the C64 (here the upper-case/graphics set):
Upper-Case/Graphics characters of the C64 by screen code, range 0-127.
The Dead Test cartridge implements just 58 characters of these (screen codes $00–$39) without any reverse video characters:
Characters implemented by the C64 Dead Test diagnostic cartridge by screen code.
As the attentive reader may observe, this only implements upper-case letters, digits, and a few punctuations and mathematical operators. $1B–$1F ( [ £ ] ↑ ← ) are taken directly from the normal character set, as are $28–$2F ( ( ) * + , − . / ). An extra blank takes the place of the "at" character ( @ ) in the normal character set at $00 (a smart move for a diagnostic cartridge, but this feature is actually never used), and the box border characters ╭ ╮ ╰ ╯ ─ │ are implemented in the range of $22–$27, where we normally find " # $ % & '. And then there’s a mysterious, C-shaped character at $21 (normally the exclamation mark ! ), which isn’t referred to anywhere in the ROM, neither as an operand nor in any data section.
(If you attempted to display any other screen codes, the fill pattern $AA, fine vertical stripes of 10101010 as in "▥", would be displayed instead, but this doesn’t happen with the cartridge.)
Visually, this is another Computer™ font, made of boxy character shapes stylized by rectangular lumps (and slightly rounded, if the resulation allows for this). There have been others, like the “901447m” character ROM for the PET:
Sample of the ‘901447m’ character ROM of unknown origin for the Commodore PET.
Clearly, these have all been inspired by the MICR (Magnetic Ink Character Recognition) character set E-13B, consisting of just 14 glyphs, the digits 0-9 and 4 additional marks:
MICR (Magnetic Ink Character Recognition) set E-18B.
The digits of the Dead Test font actually provide a pretty close representation of this, with just the shape of the digit “3” deviating somewhat for of a more boxy look:
Digits as rendered by the C64 Dead Test diagnostic cartridge.
The alphabetic characters (A–Z) align with this style, favoring a spread over a 6 × 7 pixels box centered at the top, with the characters “M” and “W” spreading in a wider 7 × 7 box to the right.
Admitteddly, the thin single-pixel vertical strokes won’t do well on a consumer-grade CRT color TV set, but, if you were a service technician or a professional field repair person with access to this cartridge, you probably also had access to a professional monitor (along with the cosy feeling of being somewhat special).
An Unexpected Out-of-Season Easter
It’s this close relation to the MICR E-18B font that brings us closer to the true nature of our mystery character #0x21, a character never to be displayed, since it isn’t referenced anwhere in the cartridge’s code:
C64 Dead Test diagnostic cartridge screen code #0x21.
So, what is this, a slightly misshaped or heavily stylized character “C”, maybe intended as part of the “chicken lips” logo, missing its second half?
No! — It’s the “transit” symbol of the MICR set, used as a delimiter for bank routing codes!
“Transit” symbol of the MICR set E-18B.
This is an explicit nod to the MICR set, and a true Easter egg, hidden...