The C64 Dead Test Font
Recorded: May 24, 2026, 6:58 a.m.
| Original | Summarized |
<Now Go Bang!> The C64 Dead Test Font Skip to main content Menu Home The C64 Dead Test Font 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, for once.(The same font, BTW, 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.) Screenshot of the C64 Dead Test diagnostic cartridge in action.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. 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. 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? “Transit” symbol of the MICR set E-18B. This is an explicit nod to the MICR set, and a true Easter egg, hidden in a font!(And its only fair and fitting that this should take the place of the exclamation mark.) Commodore pamphlet “Introducing the Commodore Max Machine™.” (1982), pages 2 & 3 of 18.→ Open in a new window/tab. · Source: archive.org. The Commodore Max, known as the Commodore Max Machine in Japan, also as the Commodore Ultimax in the USA and as the VC-10 in Germany (announced but never released), was a short-lived attempt at a low-budget home computer featuring many of the C64 core ingredients, introduced in 1982 and discontinued the same year.The Commodore Max packs the SID, the VIC II, the MOS 6510 and a single CIA along with just 4K (or 2K, depending on the source — I think, this is 2K usable memory with $0000–$01FF reserved for the zero-page and the processor stack, and $0400–$07FF reserved for the video memory, with a total amount of 4K addressable RAM in the range of $0000 to $0FFF), no user port and a membrane keyboard. Crucially, the Commodore Max doesn’t include any ROM and relies entirely on cartridge ROM. The cartridge / expansion port of the Commodore C64. Ultimax mode configures the C64 for the following memory map: $0000-$0FFF .... RAM (4K) Like on the Commodore Max, there are now just 4K of addressable RAM ($0000–$0FFF) and two addressable 8K ROM banks (ROML at $8000–$9FFF and ROMH at $E000–$FFFF). The I/O area at $D000–$DFFF conveniently remains the same as in standard C64 mode. As we may see, the built-in C64 ROMs, including the character ROM, are banked out. Moreover, ROMH crucially includes the 6510 system vectors including the RESET vector specifying the start address. Thus, the cartridge stands entirely on its own.(The outgoing signals _ROML and _ROMH select which cartrige ROM area is addressed. For an 8K cartridge, this is ROMH at $E000–$FFFF, which includes the system vectors required for start-up.) screen code $00 EAD8: 00 ; ........ screen code $01 EAE0: 7E ; .******. screen code $02 EAE8: 7E ; .******. screen code $03 EAF0: 7E ; .******. screen code $04 EAF8: 7E ; .******. screen code $05 EB00: 7E ; .******. screen code $06 EB08: 7E ; .******. screen code $07 EB10: 7E ; .******. screen code $08 EB18: 42 ; .*....*. screen code $09 EB20: 10 ; ...*.... screen code $0A EB28: 04 ; .....*.. screen code $0B EB30: 42 ; .*....*. screen code $0C EB38: 40 ; .*...... screen code $0D EB40: 43 ; .*....** screen code $0E EB48: E2 ; ***...*. screen code $0F EB50: 7E ; .******. screen code $10 EB58: 7E ; .******. screen code $11 EB60: 7E ; .******. screen code $12 EB68: 7E ; .******. screen code $13 EB70: 7E ; .******. screen code $14 EB78: 7E ; .******. screen code $15 EB80: 62 ; .**...*. screen code $16 EB88: 62 ; .**...*. screen code $17 EB90: C2 ; **....*. screen code $18 EB98: 62 ; .**...*. screen code $19 EBA0: 62 ; .**...*. screen code $1A EBA8: 7F ; .******* screen code $1B EBB0: 3C ; ..****.. screen code $1C EBB8: 0E ; ....***. screen code $1D EBC0: 3C ; ..****.. screen code $1E EBC8: 00 ; ........ screen code $1F EBD0: 00 ; ........ screen code $20 EBD8: 00 ; ........ screen code $21 EBE0: 0E ; ....***. screen code $22 EBE8: 00 ; ........ screen code $23 EBF0: 00 ; ........ screen code $24 EBF8: 18 ; ...**... screen code $25 EC00: 18 ; ...**... screen code $26 EC08: 00 ; ........ screen code $27 EC10: 18 ; ...**... screen code $28 EC18: 0C ; ....**.. screen code $29 EC20: 30 ; ..**.... screen code $2A EC28: 00 ; ........ screen code $2B EC30: 00 ; ........ screen code $2C EC38: 00 ; ........ screen code $2D EC40: 00 ; ........ screen code $2E EC48: 00 ; ........ screen code $2F EC50: 00 ; ........ screen code $30 EC58: 7E ; .******. screen code $31 EC60: 30 ; ..**.... screen code $32 EC68: 7E ; .******. screen code $33 EC70: 7E ; .******. screen code $34 EC78: 60 ; .**..... screen code $35 EC80: 7E ; .******. screen code $36 EC88: 78 ; .****... screen code $37 EC90: 7E ; .******. screen code $38 EC98: 3C ; ..****.. screen code $39 ECA0: 7E ; .******. Notably, the order (with the exception of the border characters) follows the usual PETSCII screen code order. However, since we’re no longer relying on any C64 ROM, the order and what screen codes actually represent what is merely convention at this point. We simply put a code in the video RAM at $0400–$07FF and whatever character matrices are found at the corresponding address in the cartridge ROM are displayed by the hardware, which is in this case configured by the cartridge code to look up the respective character matrices at $EAD8. In Ultimax mode, there is no further meaning to screen codes implied. C64, upper-case / graphics set. C64, lower-case / upper-case set. And for the PET (similar for the VIC-20, but with “£” instead of the backslash and including reverse character forms), available in the old PET 2001 format and for newer PETs: PET, upper-case / graphics set. PET, lower-case / upper-case set. PET, upper-case / katakana set. dead-test-font-roms.zip (zip archive, 30.3 KB, includes 7 ROM images and read-me file). — And that’s all folks. — Norbert Landsteiner,Vienna, 2026-05-24 © 1999–2026 N. Landsteiner, mass:werk – media environments RSS-Feed |
A detailed examination of the font embedded within the Commodore 64 Dead Test diagnostic cartridge reveals a unique implementation that provides insight into the machine's architecture and its relationship with other systems. The author addresses a notable omission in existing documentation by dissecting the display font used by this cartridge, which is unique and instantly recognizable, and explores its derivation from earlier character sets. The cartridge utilizes an embedded ROM for its display, allowing it to operate independently without relying on the C64's built-in Character ROMs, a feature enabled by the cartridge's design. The Dead Test cartridge implements only fifty-eight characters corresponding to screen codes from zero to thirty-nine, focusing on uppercase letters, digits, and basic mathematical operators. The visual appearance of this font is characterized by boxy, rectangular character shapes, which are implicitly inspired by the MICR Magnetic Ink Character Recognition set E-13B, featuring a system of rectangular lumps. The implementation deliberately deviates from the standard C64 character set; for instance, the digit three is rendered with a boxier appearance, and certain letters like M and W occupy wider boxes. This modification, while aesthetically distinct, appeals to a niche audience familiar with professional display systems, suggesting a design choice that prioritizes a specific, stylized aesthetic over standard character representation. A significant element of this exploration is the discovery of an unexpected Easter egg within the font structure, specifically related to the screen code thirty-one ($\text{0x21}$). This character is not referenced anywhere within the cartridge's code, yet its representation is a C-shaped symbol known as the "transit" symbol from the MICR set E-18B, which typically functions as a delimiter for bank routing codes. This inclusion serves as a hidden nod to the underlying character system, establishing a complex layer of reference within the embedded graphics. The functionality of the cartridge hinges on the C64's dual architecture, which the author details by explaining how the system can operate as both a standard Commodore 64 and a Commodore Max machine. This compatibility mode is triggered by specific signals ($\text{GAME}$ and $\text{XROM}$) on the expansion port, which switch the C64 into Ultimax mode. In this mode, the memory addressing is reorganized, allowing the cartridge to control memory banks, including the $\text{ROML}$ and $\text{ROMH}$ areas, which contain the necessary system vectors for startup. The Dead Test cartridge leverages this mechanism by configuring itself as an eight kilo-byte cartridge that uses the $\text{ROMH}$ area ($\text{E000–\text{FFFF}}$) for its data and system vectors, thereby operating autonomously from the built-in C64 ROMs. The actual font data is stored in the cartridge ROM starting at memory address $\text{EAD8}$, with the remaining space filled with the value $\text{AA}$. The data maps screen codes to character matrices. The order of these screen codes follows the standard PETSCII screen code sequence, although the actual interpretation of these codes is determined by the cartridge rather than the C64's internal ROMs. This configuration demonstrates that once the system relies on cartridge ROM rather than built-in ROMs, the traditional meaning of screen codes becomes conventional rather than strictly defined by the original hardware specification. Ultimately, the work provides a collection of font ROMs for various Commodore systems, including the C64, VIC-20, and PET, offering users the ability to implement this unique Dead Test font across multiple platforms. |