MagicDesk-like External ROM cartridge for C128

PROJECT PAGE

KiCad project files and schematic: https://github.com/ytmytm/c128-magicdesk-external-rom

DESCRIPTION

This a clone of MagicDesk 512k modified to work in C128 mode and map 32K of ROM at a time.

The main difference to C64 version is that this cartridge is meant for C128, so /EXROM signal is no longer connected to prevent from entering C64 mode automatically.

Two diodes and a pullup resistor perform AND function on /ROML and /ROMH to map 32K at a time ($8000-$FFFF).

Because the bank size is now 32K instead of 8K the lowest two bits of control register are not connected.

The smallest EPROM you can use is 27C512 (64K), and the largest one is 27C040 (512 KB). With two of those piggy-backed one over another and a piece of wire you can expand the board to full 1MB.

See the MagicDesk 512k project page for details about jumper configuration for various EEPROM/EPROM/FLASH chips and enclosure options: https://github.com/msolajic/c64-magic-desk-512k

COMPONENTS

1x 74LS02

1x 74LS273

1x 10K resistor

2x 1N4148 diode

1x EPROM (from 27C512 to 27C040 or their FLASH / EEPROM variants)

1x Tact Switch (6x6mm, horizontal or vertical)